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• Decrementing/Incrementing loop variable inside for loop. Is this code smell?

  - by FairDune

  I have to read lines from a text file in sequential order. The file is a custom text format that contains sections. If some sections are out of order, I would like to look for the starting of the next valid section and continue processing. Currently, I have some code that looks like this: for (int currentLineIndex=0; currentLineIndex < lines.Count; currentLineIndex++ ) { //Process section here if( out_of_order_condition ) { currentLineIndex--;//Stay on the same line in the next iteration because this line may be the start of a valid section. continue; } } Is this code smell?

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• Measuring execution time of selected loops

  - by user95281

  I want to measure the running times of selected loops in a C program so as to see what percentage of the total time for executing the program (on linux) is spent in these loops. I should be able to specify the loops for which the performance should be measured. I have tried out several tools (vtune, hpctoolkit, oprofile) in the last few days and none of them seem to do this. They all find the performance bottlenecks and just show the time for those. Thats because these tools only store the time taken that is above a threshold (~1ms). So if one loop takes lesser time than that then its execution time won't be reported. The basic block counting feature of gprof depends on a feature in older compilers thats not supported now. I could manually write a simple timer using gettimeofday or something like that but for some cases it won't give accurate results. For ex: for (i = 0; i < 1000; ++i) { for (j = 0; j < N; ++j) { //do some work here } } Now here I want to measure the total time spent in the inner loop and I will have to put a call to gettimeofday inside the first loop. So gettimeofday itself will get called a 1000 times which introduces its own overhead and the result will be inaccurate.

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• Random Page Cost and Planning

  - by Dave Jarvis

  A query (see below) that extracts climate data from weather stations within a given radius of a city using the dates for which those weather stations actually have data. The query uses the table's only index, rather effectively: CREATE UNIQUE INDEX measurement_001_stc_idx ON climate.measurement_001 USING btree (station_id, taken, category_id); Reducing the server's configuration value for random_page_cost from 2.0 to 1.1 had a massive performance improvement for the given range (nearly an order of magnitude) because it suggested to PostgreSQL that it should use the index. While the results now return in 5 seconds (down from ~85 seconds), problematic lines remain. Bumping the query's end date by a single year causes a full table scan: sc.taken_start >= '1900-01-01'::date AND sc.taken_end <= '1997-12-31'::date AND How do I persuade PostgreSQL to use the indexes regardless of years between the two dates? (A full table scan against 43 million rows is probably not the best plan.) Find the EXPLAIN ANALYSE results below the query. Thank you! Query SELECT extract(YEAR FROM m.taken) AS year, avg(m.amount) AS amount FROM climate.city c, climate.station s, climate.station_category sc, climate.measurement m WHERE c.id = 5182 AND earth_distance( ll_to_earth(c.latitude_decimal,c.longitude_decimal), ll_to_earth(s.latitude_decimal,s.longitude_decimal)) / 1000 <= 30 AND s.elevation BETWEEN 0 AND 3000 AND s.applicable = TRUE AND sc.station_id = s.id AND sc.category_id = 1 AND sc.taken_start >= '1900-01-01'::date AND sc.taken_end <= '1996-12-31'::date AND m.station_id = s.id AND m.taken BETWEEN sc.taken_start AND sc.taken_end AND m.category_id = sc.category_id GROUP BY extract(YEAR FROM m.taken) ORDER BY extract(YEAR FROM m.taken) 1900 to 1996: Index "Sort (cost=1348597.71..1348598.21 rows=200 width=12) (actual time=2268.929..2268.935 rows=92 loops=1)" " Sort Key: (date_part('year'::text, (m.taken)::timestamp without time zone))" " Sort Method: quicksort Memory: 32kB" " -> HashAggregate (cost=1348586.56..1348590.06 rows=200 width=12) (actual time=2268.829..2268.886 rows=92 loops=1)" " -> Nested Loop (cost=0.00..1344864.01 rows=744510 width=12) (actual time=0.807..2084.206 rows=134893 loops=1)" " Join Filter: ((m.taken >= sc.taken_start) AND (m.taken <= sc.taken_end) AND (sc.station_id = m.station_id))" " -> Nested Loop (cost=0.00..12755.07 rows=1220 width=18) (actual time=0.502..521.937 rows=23 loops=1)" " Join Filter: ((sec_to_gc(cube_distance((ll_to_earth((c.latitude_decimal)::double precision, (c.longitude_decimal)::double precision))::cube, (ll_to_earth((s.latitude_decimal)::double precision, (s.longitude_decimal)::double precision))::cube)) / 1000::double precision) <= 30::double precision)" " -> Index Scan using city_pkey1 on city c (cost=0.00..2.47 rows=1 width=16) (actual time=0.014..0.015 rows=1 loops=1)" " Index Cond: (id = 5182)" " -> Nested Loop (cost=0.00..9907.73 rows=3659 width=34) (actual time=0.014..28.937 rows=3458 loops=1)" " -> Seq Scan on station_category sc (cost=0.00..970.20 rows=3659 width=14) (actual time=0.008..10.947 rows=3458 loops=1)" " Filter: ((taken_start >= '1900-01-01'::date) AND (taken_end <= '1996-12-31'::date) AND (category_id = 1))" " -> Index Scan using station_pkey1 on station s (cost=0.00..2.43 rows=1 width=20) (actual time=0.004..0.004 rows=1 loops=3458)" " Index Cond: (s.id = sc.station_id)" " Filter: (s.applicable AND (s.elevation >= 0) AND (s.elevation <= 3000))" " -> Append (cost=0.00..1072.27 rows=947 width=18) (actual time=6.996..63.199 rows=5865 loops=23)" " -> Seq Scan on measurement m (cost=0.00..25.00 rows=6 width=22) (actual time=0.000..0.000 rows=0 loops=23)" " Filter: (m.category_id = 1)" " -> Bitmap Heap Scan on measurement_001 m (cost=20.79..1047.27 rows=941 width=18) (actual time=6.995..62.390 rows=5865 loops=23)" " Recheck Cond: ((m.station_id = sc.station_id) AND (m.taken >= sc.taken_start) AND (m.taken <= sc.taken_end) AND (m.category_id = 1))" " -> Bitmap Index Scan on measurement_001_stc_idx (cost=0.00..20.55 rows=941 width=0) (actual time=5.775..5.775 rows=5865 loops=23)" " Index Cond: ((m.station_id = sc.station_id) AND (m.taken >= sc.taken_start) AND (m.taken <= sc.taken_end) AND (m.category_id = 1))" "Total runtime: 2269.264 ms" 1900 to 1997: Full Table Scan "Sort (cost=1370192.26..1370192.76 rows=200 width=12) (actual time=86165.797..86165.809 rows=94 loops=1)" " Sort Key: (date_part('year'::text, (m.taken)::timestamp without time zone))" " Sort Method: quicksort Memory: 32kB" " -> HashAggregate (cost=1370181.12..1370184.62 rows=200 width=12) (actual time=86165.654..86165.736 rows=94 loops=1)" " -> Hash Join (cost=4293.60..1366355.81 rows=765061 width=12) (actual time=534.786..85920.007 rows=139721 loops=1)" " Hash Cond: (m.station_id = sc.station_id)" " Join Filter: ((m.taken >= sc.taken_start) AND (m.taken <= sc.taken_end))" " -> Append (cost=0.00..867005.80 rows=43670150 width=18) (actual time=0.009..79202.329 rows=43670079 loops=1)" " -> Seq Scan on measurement m (cost=0.00..25.00 rows=6 width=22) (actual time=0.001..0.001 rows=0 loops=1)" " Filter: (category_id = 1)" " -> Seq Scan on measurement_001 m (cost=0.00..866980.80 rows=43670144 width=18) (actual time=0.008..73312.008 rows=43670079 loops=1)" " Filter: (category_id = 1)" " -> Hash (cost=4277.93..4277.93 rows=1253 width=18) (actual time=534.704..534.704 rows=25 loops=1)" " -> Nested Loop (cost=847.87..4277.93 rows=1253 width=18) (actual time=415.837..534.682 rows=25 loops=1)" " Join Filter: ((sec_to_gc(cube_distance((ll_to_earth((c.latitude_decimal)::double precision, (c.longitude_decimal)::double precision))::cube, (ll_to_earth((s.latitude_decimal)::double precision, (s.longitude_decimal)::double precision))::cube)) / 1000::double precision) <= 30::double precision)" " -> Index Scan using city_pkey1 on city c (cost=0.00..2.47 rows=1 width=16) (actual time=0.012..0.014 rows=1 loops=1)" " Index Cond: (id = 5182)" " -> Hash Join (cost=847.87..1352.07 rows=3760 width=34) (actual time=6.427..35.107 rows=3552 loops=1)" " Hash Cond: (s.id = sc.station_id)" " -> Seq Scan on station s (cost=0.00..367.25 rows=7948 width=20) (actual time=0.004..23.529 rows=7949 loops=1)" " Filter: (applicable AND (elevation >= 0) AND (elevation <= 3000))" " -> Hash (cost=800.87..800.87 rows=3760 width=14) (actual time=6.416..6.416 rows=3552 loops=1)" " -> Bitmap Heap Scan on station_category sc (cost=430.29..800.87 rows=3760 width=14) (actual time=2.316..5.353 rows=3552 loops=1)" " Recheck Cond: (category_id = 1)" " Filter: ((taken_start >= '1900-01-01'::date) AND (taken_end <= '1997-12-31'::date))" " -> Bitmap Index Scan on station_category_station_category_idx (cost=0.00..429.35 rows=6376 width=0) (actual time=2.268..2.268 rows=6339 loops=1)" " Index Cond: (category_id = 1)" "Total runtime: 86165.936 ms"

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• Avoiding nesting two for loops

  - by chavanak

  Hi, Please have a look at the code below: import string from collections import defaultdict first_complex=open( "residue_a_chain_a_b_backup.txt", "r" ) first_complex_lines=first_complex.readlines() first_complex_lines=map( string.strip, first_complex_lines ) first_complex.close() second_complex=open( "residue_a_chain_a_c_backup.txt", "r" ) second_complex_lines=second_complex.readlines() second_complex_lines=map( string.strip, second_complex_lines ) second_complex.close() list_1=[] list_2=[] for x in first_complex_lines: if x[0]!="d": list_1.append( x ) for y in second_complex_lines: if y[0]!="d": list_2.append( y ) j=0 list_3=[] list_4=[] for a in list_1: pass for b in list_2: pass if a==b: list_3.append( a ) kvmap=defaultdict( int ) for k in list_3: kvmap[k]+=1 print kvmap Normally I use izip or izip_longest to club two for loops, but this time the length of the files are different. I don't want a None entry. If I use the above method, the run time becomes incremental and useless. How am I supposed to get the two for loops going? Cheers, Chavanak

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• Erlang message loops

  - by Roger Alsing

  How does message loops in erlang work, are they sync when it comes to processing messages? As far as I understand, the loop will start by "receive"ing a message and then perform something and hit another iteration of the loop. So that has to be sync? right? If multiple clients send messages to the same message loop, then all those messages are queued and performed one after another, or? To process multiple messages in parallell, you would have to spawn multiple message loops in different processes, right? Or did I misunderstand all of it?

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• Nested foreach loops for associative array combinations

  - by JohnL

  I have an associative array as follows: $myarray = array('a'=>array(), 'b'=>array(), 'c'=>array(), 'd'=>array()); I want to be able to get all pairs of elements in the array. If it wasn't an associative array, I would use nested for loops, like: for($i=0; $i<count($myarray); $i++) { for($j=$i+1; $j<count($myarray); $j++) { do_something($myarray[$i], $myarray[$j]); } } I have looked at using foreach loops, but as the inner loop goes through ALL elements, some pairs are repeated. Is there a way to do this? Thanks!

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• Best practice for creating objects used in for/foreach loops

  - by StupidDeveloper

  Hi! What's the best practice for dealing with objects in for or foreach loops? Should we create one object outside the loops and recreate it all over again (using new... ) or create new one for every loop iteration? Example: foreach(var a in collection) { SomeClass sc = new SomeClass(); sc.id = a; sc.Insert(); } or SomeClass sc = null; foreach(var a in collection) { sc = new SomeClass(); sc.id = a; sc.Insert(); } Which is better?

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• Writing loops with i++ or ++i [duplicate]

  - by Nonesuch

  This question already has an answer here: Why use ++i instead of i++ in cases where the value is not used anywhere else in the statement? 6 answers format of for loops 31 answers I have a question about writing loops. I always begin with (int i=0; i<10; i++) But I see many experts begin with (int i=0; i<10; ++i) Is there there any real difference, or they are same? Of course, I know the difference between pre-increment and post-increment. I mean which one I should use when writing the loop? or it depends. Thanks!

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• Loops on a Matlab program

  - by lebland-matlab

  I have 3 sets of 10 vectors each, and I want to take 2 vectors from the first set , 2 vectors from the second set and 3 vectors from the third set . My goal is to make a loop to implement the following program, knowing that after each calculation, the result shall be saved in a new file. My problem is that I can not handle the indices included in the strings. I try to use multiple loops to scan the 3 sets in the order of indices. loops should contain the following program clc; clear all; load('C:\Users\Documents\MATLAB\myFile\matrice_F.mat'); load('C:\Users\Documents\MATLAB\myFile\matrice_G.mat'); F = m_F; G = m_G; load('C:\Users\Documents\MATLAB\myFile\matrice_J.mat'); load('C:\Users\Documents\MATLAB\myFile\matrice_K.mat'); J = m_J; K = m_K; load('C:\Users\Documents\MATLAB\myFile\matrice_N.mat'); load('C:\Users\Documents\MATLAB\myFile\matrice_O.mat'); load('C:\Users\Documents\MATLAB\myFile\matrice_P.mat'); N = m_N ; O = m_O; P = m_P; [A,B,C,D,E] = myFun(F,G,J,K,N,O,P); file_name = 'matrice_final.mat'; save(file_name,'A','B','C','D','E');

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• Types of Nested Loops in JAVA

  - by dominoos

  Hi guys. I have a simple question. I have to find out many nested loops as possible in java. I have something like for loop and if statement inside. i know that we can do like if{if{if{if{ something like that too. just need some more idea of more types of nested loops. if you can write down some examples. I'll be very glad. thank you. public class Test { public static void main (String []args) { int i = 0; for(int j = 1; j <= 5; j++) { if(j == 1 || j == 5) { i = 4; } else { i = 1; } for(int x = 0; x < i; x++) { System.out.print("**"); } System.out.println(); } } }

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• Problems breaking out of nested loops

  - by user1040281

  I have problems breaking out off these nested loops correctly. What the code is trying to do is to indicate that a customer has rented a certain movie. Both the movie and customer are compared to properties of arraylist objects and then if all checks out the name property and ID property of a movie object are added as a string to another arraylist. All this works correctly as long as I use the first movie (from movies) and the first customer (from customers) but if I try renting other movies further down my arraylist with other customers then it adds the rented movie to the customerRentedMovies arraylist but prints out the "else message". I figure I need to break out of the foreach(blabla) loops aswell? or could goto be used? Comments was removed (looked kinda messy, can explain further if needed) public void RentMovie(string titel, int movieID, string name, int customerID) { foreach (Customer customer in customers) { if (name == customer.Name && customerID == customer.CustomerID) { foreach (MovieInfo movie in movies) { if (titel == movie.Titel && movieID == movie.MovieID) { movie.rented = true; string rentedMovie = string.Format("{0} ID: {1}", movie.Titel, movie.MovieID); customer.customerRentedMovies.Add(rentedMovie); break; } else { Console.WriteLine("No movie with that titel and ID!"); } } break; } else { Console.WriteLine("No customer with that ID and name"); } } }

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• ios7 loops on the "trust this computer" dialog

  - by gcb

  trying to transfer files to the work ipad via my debian7 box. When i plug it on the computer usb port, it shows the dialog about trusting this computer, and the computer shows a gnome alert about the ipad being locked and that i should unlock it and try again. i press "trust" on the ipad and try again on gnome. and it starts again. over and over. endlessly. there are dozen threads about this on apple support forums. no solution. just dozens of "me too" flags. e.g. https://discussions.apple.com/message/23082859#23082859 (44 me-too, 2k views) here is the log/messages i get Oct 23 21:17:39 dotmatrix kernel: [ 1928.517766] usb 2-1.7: USB disconnect, device number 16 Oct 23 21:17:39 dotmatrix kernel: [ 1928.715441] usb 2-1.7: new high-speed USB device number 17 using ehci_hcd Oct 23 21:17:40 dotmatrix kernel: [ 1928.811031] usb 2-1.7: New USB device found, idVendor=05ac, idProduct=12ab Oct 23 21:17:40 dotmatrix kernel: [ 1928.811036] usb 2-1.7: New USB device strings: Mfr=1, Product=2, SerialNumber=3 Oct 23 21:17:40 dotmatrix kernel: [ 1928.811039] usb 2-1.7: Product: iPad Oct 23 21:17:40 dotmatrix kernel: [ 1928.811041] usb 2-1.7: Manufacturer: Apple Inc. Oct 23 21:17:40 dotmatrix kernel: [ 1928.811043] usb 2-1.7: SerialNumber: fec5e0f6a6fa18a936de3c53af661051d290275e Oct 23 21:17:40 dotmatrix mtp-probe: checking bus 2, device 17: "/sys/devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1.7" Oct 23 21:17:40 dotmatrix mtp-probe: bus: 2, device: 17 was not an MTP device Oct 23 21:17:43 dotmatrix kernel: [ 1932.346505] usb 2-1.7: USB disconnect, device number 17 If i never press the trust dialog it will stay there until i remove the cable. but the logs shows that it gave up 3sec after the cable was connected.

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• Parallel shell loops

  - by brubelsabs

  Hi, I want to process many files and since I've here a bunch of cores I want to do it in parallel: for i in *.myfiles; do do_something $i `derived_params $i` other_params; done I know of a Makefile solution but my commands needs the arguments out of the shell globbing list. What I found is: > function pwait() { > while [ $(jobs -p | wc -l) -ge $1 ]; do > sleep 1 > done > } > To use it, all one has to do is put & after the jobs and a pwait call, the parameter gives the number of parallel processes: > for i in *; do > do_something $i & > pwait 10 > done But this doesn't work very well, e.g. I tried it with e.g. a for loop converting many files but giving me error and left jobs undone. I can't belive that this isn't done yet since the discussion on zsh mailing list is so old by now. So do you know any better?

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• How does an optimizing compiler react to a program with nested loops?

  - by D.Singh

  Say you have a bunch of nested loops. public void testMethod() { for(int i = 0; i<1203; i++){ //some computation for(int k=2; k<123; k++){ //some computation for(int j=2; j<12312; j++){ //some computation for(int l=2; l<123123; l++){ //some computation for(int p=2; p<12312; p++){ //some computation } } } } } } When the above code reaches the stage where the compiler will try to optimize it (I believe it's when the intermediate language needs to converted to machine code?), what will the compiler try to do? Is there any significant optimization that will take place? I understand that the optimizer will break up the loops by means of loop fission. But this is only per loop isn't it? What I mean with my question is will it take any action exclusively based on seeing the nested loops? Or will it just optimize the loops one by one? If the Java VM complicates the explanation then please just assume that it's C or C++ code.

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• int, short, byte performance in back-to-back for-loops

  - by runrunraygun

  (background: http://stackoverflow.com/questions/1097467/why-should-i-use-int-instead-of-a-byte-or-short-in-c) To satisfy my own curiosity about the pros and cons of using the "appropriate size" integer vs the "optimized" integer i wrote the following code which reinforced what I previously held true about int performance in .Net (and which is explained in the link above) which is that it is optimized for int performance rather than short or byte. DateTime t; long a, b, c; t = DateTime.Now; for (int index = 0; index < 127; index++) { Console.WriteLine(index.ToString()); } a = DateTime.Now.Ticks - t.Ticks; t = DateTime.Now; for (short index = 0; index < 127; index++) { Console.WriteLine(index.ToString()); } b=DateTime.Now.Ticks - t.Ticks; t = DateTime.Now; for (byte index = 0; index < 127; index++) { Console.WriteLine(index.ToString()); } c=DateTime.Now.Ticks - t.Ticks; Console.WriteLine(a.ToString()); Console.WriteLine(b.ToString()); Console.WriteLine(c.ToString()); This gives roughly consistent results in the area of... ~950000 ~2000000 ~1700000 which is in line with what i would expect to see. However when I try repeating the loops for each data type like this... t = DateTime.Now; for (int index = 0; index < 127; index++) { Console.WriteLine(index.ToString()); } for (int index = 0; index < 127; index++) { Console.WriteLine(index.ToString()); } for (int index = 0; index < 127; index++) { Console.WriteLine(index.ToString()); } a = DateTime.Now.Ticks - t.Ticks; the numbers are more like... ~4500000 ~3100000 ~300000 Which I find puzzling. Can anyone offer an explanation? NOTE: In the interest of compairing like for like i've limited the loops to 127 because of the range of the byte value type. Also this is an act of curiosity not production code micro-optimization.

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• Strange: Planner takes decision with lower cost, but (very) query long runtime

  - by S38

  Facts: PGSQL 8.4.2, Linux I make use of table inheritance Each Table contains 3 million rows Indexes on joining columns are set Table statistics (analyze, vacuum analyze) are up-to-date Only used table is "node" with varios partitioned sub-tables Recursive query (pg = 8.4) Now here is the explained query: WITH RECURSIVE rows AS ( SELECT * FROM ( SELECT r.id, r.set, r.parent, r.masterid FROM d_storage.node_dataset r WHERE masterid = 3533933 ) q UNION ALL SELECT * FROM ( SELECT c.id, c.set, c.parent, r.masterid FROM rows r JOIN a_storage.node c ON c.parent = r.id ) q ) SELECT r.masterid, r.id AS nodeid FROM rows r QUERY PLAN ----------------------------------------------------------------------------------------------------------------------------------------------------------------- CTE Scan on rows r (cost=2742105.92..2862119.94 rows=6000701 width=16) (actual time=0.033..172111.204 rows=4 loops=1) CTE rows -> Recursive Union (cost=0.00..2742105.92 rows=6000701 width=28) (actual time=0.029..172111.183 rows=4 loops=1) -> Index Scan using node_dataset_masterid on node_dataset r (cost=0.00..8.60 rows=1 width=28) (actual time=0.025..0.027 rows=1 loops=1) Index Cond: (masterid = 3533933) -> Hash Join (cost=0.33..262208.33 rows=600070 width=28) (actual time=40628.371..57370.361 rows=1 loops=3) Hash Cond: (c.parent = r.id) -> Append (cost=0.00..211202.04 rows=12001404 width=20) (actual time=0.011..46365.669 rows=12000004 loops=3) -> Seq Scan on node c (cost=0.00..24.00 rows=1400 width=20) (actual time=0.002..0.002 rows=0 loops=3) -> Seq Scan on node_dataset c (cost=0.00..55001.01 rows=3000001 width=20) (actual time=0.007..3426.593 rows=3000001 loops=3) -> Seq Scan on node_stammdaten c (cost=0.00..52059.01 rows=3000001 width=20) (actual time=0.008..9049.189 rows=3000001 loops=3) -> Seq Scan on node_stammdaten_adresse c (cost=0.00..52059.01 rows=3000001 width=20) (actual time=3.455..8381.725 rows=3000001 loops=3) -> Seq Scan on node_testdaten c (cost=0.00..52059.01 rows=3000001 width=20) (actual time=1.810..5259.178 rows=3000001 loops=3) -> Hash (cost=0.20..0.20 rows=10 width=16) (actual time=0.010..0.010 rows=1 loops=3) -> WorkTable Scan on rows r (cost=0.00..0.20 rows=10 width=16) (actual time=0.002..0.004 rows=1 loops=3) Total runtime: 172111.371 ms (16 rows) (END) So far so bad, the planner decides to choose hash joins (good) but no indexes (bad). Now after doing the following: SET enable_hashjoins TO false; The explained query looks like that: QUERY PLAN ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- CTE Scan on rows r (cost=15198247.00..15318261.02 rows=6000701 width=16) (actual time=0.038..49.221 rows=4 loops=1) CTE rows -> Recursive Union (cost=0.00..15198247.00 rows=6000701 width=28) (actual time=0.032..49.201 rows=4 loops=1) -> Index Scan using node_dataset_masterid on node_dataset r (cost=0.00..8.60 rows=1 width=28) (actual time=0.028..0.031 rows=1 loops=1) Index Cond: (masterid = 3533933) -> Nested Loop (cost=0.00..1507822.44 rows=600070 width=28) (actual time=10.384..16.382 rows=1 loops=3) Join Filter: (r.id = c.parent) -> WorkTable Scan on rows r (cost=0.00..0.20 rows=10 width=16) (actual time=0.001..0.003 rows=1 loops=3) -> Append (cost=0.00..113264.67 rows=3001404 width=20) (actual time=8.546..12.268 rows=1 loops=4) -> Seq Scan on node c (cost=0.00..24.00 rows=1400 width=20) (actual time=0.001..0.001 rows=0 loops=4) -> Bitmap Heap Scan on node_dataset c (cost=58213.87..113214.88 rows=3000001 width=20) (actual time=1.906..1.906 rows=0 loops=4) Recheck Cond: (c.parent = r.id) -> Bitmap Index Scan on node_dataset_parent (cost=0.00..57463.87 rows=3000001 width=0) (actual time=1.903..1.903 rows=0 loops=4) Index Cond: (c.parent = r.id) -> Index Scan using node_stammdaten_parent on node_stammdaten c (cost=0.00..8.60 rows=1 width=20) (actual time=3.272..3.273 rows=0 loops=4) Index Cond: (c.parent = r.id) -> Index Scan using node_stammdaten_adresse_parent on node_stammdaten_adresse c (cost=0.00..8.60 rows=1 width=20) (actual time=4.333..4.333 rows=0 loops=4) Index Cond: (c.parent = r.id) -> Index Scan using node_testdaten_parent on node_testdaten c (cost=0.00..8.60 rows=1 width=20) (actual time=2.745..2.746 rows=0 loops=4) Index Cond: (c.parent = r.id) Total runtime: 49.349 ms (21 rows) (END) - incredibly faster, because indexes were used. Notice: Cost of the second query ist somewhat higher than for the first query. So the main question is: Why does the planner make the first decision, instead of the second? Also interesing: Via SET enable_seqscan TO false; i temp. disabled seq scans. Than the planner used indexes and hash joins, and the query still was slow. So the problem seems to be the hash join. Maybe someone can help in this confusing situation? thx, R.

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• Stopping infinite loops of alerts in Mozilla

  - by Christy John

  This may be dumb question. But somehow this engaged me for sometime and after some basic research I couldn't find an answer. I was learning JavaScript and a code I wrote had an error and has been outputting infinite loops of alerts. I tried the normal shortcuts like Ctrl + C and Ctrl + Z but they didn't work. So I was thinking if there is any solution to this other than ending the browser process (like by doing a Ctrl + Alt + Del).

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• Understanding Scope on Scala's For Loops (For Comprehension)

  - by T. Stone

  In Chapter 3 of Programming Scala, the author gives two examples of for loops / for comprehensions, but switches between using ()'s and {}'s. Why is this the case, as these inherently look like they're doing the same thing? Is there a reason breed <- dogBreeds is on the 2nd line in example #2? // #1 ()'s for (breed <- dogBreeds if breed.contains("Terrier"); if !breed.startsWith("Yorkshire") ) println(breed) // #2 {}'s for { breed <- dogBreeds upcasedBreed = breed.toUpperCase() } println(upcasedBreed)

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• Do something every 3 loops in django-templates?

  - by eos87

  hi people, I wanna make change in css class every 3 loops. In the first three I want to use the CSS class A, in the next three I want to use the CSS class B, in the next three I want to use the CSS class A again and so on. can anyone help? Thanks

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• Introduction to vectorizing in MATLAB - any good tutorials?

  - by Gacek

  I'm looking for any good tutorials on vectorizing (loops) in MATLAB. I have quite simple algorithm, but it uses two for loops. I know that it should be simple to vectorize it and I would like to learn how to do it instead of asking you for the solution. But to let you know what problem I have, so you would be able to suggest best tutorials that are showing how to solve similar problems, here's the outline of my problem: B = zeros(size(A)); % //A is a given matrix. for i=1:size(A,1) for j=1:size(A,2) H = ... %// take some surrounding elements of the element at position (i,j) (i.e. using mask 3x3 elements) B(i,j) = computeSth(H); %// compute something on selected elements and place it in B end end So, I'm NOT asking for the solution. I'm asking for a good tutorials, examples of vectorizing loops in MATLAB. I would like to learn how to do it and do it on my own.

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• Simulating C-style for loops in python

  - by YGA

  (even the title of this is going to cause flames, I realize) Python made the deliberate design choice to have the for loop use explicit iterables, with the benefit of considerably simplified code in most cases. However, sometimes it is quite a pain to construct an iterable if your test case and update function are complicated, and so I find myself writing the following while loops: val = START_VAL while <awkward/complicated test case>: # do stuff ... val = <awkward/complicated update> The problem with this is that the update is at the bottom of the while block, meaning that if I want to have a continue embedded somewhere in it I have to: use duplicate code for the complicated/awkard update, AND run the risk of forgetting it and having my code infinite loop I could go the route of hand-rolling a complicated iterator: def complicated_iterator(val): while <awkward/complicated test case>: yeild val val = <awkward/complicated update> for val in complicated_iterator(start_val): if <random check>: continue # no issues here # do stuff This strikes me as waaaaay too verbose and complicated. Do folks in stack overflow have a simpler suggestion?

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• help understanding the concept of javascript callbacks with node.js, especially in loops

  - by Mr JSON

  hi I am just starting with node.js. I have done a little ajax stuff but nothing too complicated so callbacks are still kind of over my head. I looked at async but all I need is to run a few functions sequentially. I basically have something that pulls some json from an api, creates a new one and then does something with that. obviously i can't just run it because it runs everything at once and has an empty json. mostly they have to go sequentially but if while pulling a json from the api it can pull other json while it's waiting that is fine. I just got confused when putting the callback in a loop. what do I do with the index? i think i have seen some places that use callback inside the loop as kind of a recusive function and don't use for loops at all. simple examples would help alot thanks!

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• from loop to Nested loops ?

  - by WM

  I have this program that returns a factorial of N. For example, when entering 4,,, it will give 1! , 2! , 3! How could I convert this to use nested loops? public class OneForLoop { public static void main(String[] args) { Scanner input = new Scanner(System.in); System.out.print("Enter a number : "); int N = input.nextInt(); int factorial = 1; for(int i = 1; i < N; i++) { factorial *= i; System.out.println(i + "! = " + factorial); } } }

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• Best way to implement nested loops in a view in asp.net mvc 2

  - by Junior Ewing

  Hi, Trying to implement some nested loops that are spitting out good old nested html table data. So the question is; What is the best way to loop through lists and nested lists in order to produce easily maintainable code. It can get quite narly quite fast when working with multiple nested tables or lists. Should I make use of a HTML helper, or make something with the ViewModel to simplify this? A requirement is if there are no children at a node there should be an empty row on that spot with some links for creation and into other parts of the system.

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• Interaction between for loops with clock function?!

  - by learningtolive

  Can someone explain me the exact interaction in context of delay between the two for loops with clock function. How does for1 interact with for2 on the cout statement(30 on 640000000)? start=clock(); cout<<endl<<start<<endl; for(delay=0; delay<30; delay++) for(i=0; i<640000000; i++); end=clock(); cout<<end<<endl; cout<<"Num of ticks for non reg-loop: "; cout<<end-start<<'\n';

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