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• How to find length of JSON using JSON.parse?

  - by Amol

  I have a Json like this {"0":{"parent_id":1649,"id":"1803","last_update_on":"2010-12-24 07:01:49","message":"dhb;lxd","created_by_id":"21","created_by_name":"Amol Deshpande"}}. So ideally i should get length as 1 considering i have only 1 value on 0th location. what if i have a JSON like this {"0":{"parent_id":1649,"id":"1803","last_update_on":"2010-12-24 07:01:49","message":"dhb;lxd","created_by_id":"21","created_by_name":"Amol Deshpande"},"1":{"parent_id":1649,"id":"1804","last_update_on":"2010-12-24 07:02:49","message":"amol","created_by_id":"21","created_by_name":"Amol Deshpande"}} I am getting the value as undefined if i do alert(response.length); where response is my JSON as mentioned above Any suggestions?

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• What is the length of time to send a list of 200,000 integers from a client's browser to an internet

  - by indiehacker

  Over the connections that most people in the USA have in their homes, what is the approximate length of time to send a list of 200,000 integers from a client's browser to an internet sever (say Google app engine)? Does it change much if the data is sent from an iPhone? How does the length of time increase as the size of the integer list increases (say with a list of a million integers) ? Context: I wasn't sure if I should write code to do some simple computations and sorting of such lists for the browser in javascript or for the server in python, so I wanted to explore this issue of how long it takes to send the output data from a browser to a server over the web in order to help me decide where (client's browser or app engine server) is the best place for such computations to be processed.

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• Best way to test for a variable's existence in PHP; isset() is clearly broken

  - by chazomaticus

  From the isset() docs: isset() will return FALSE if testing a variable that has been set to NULL. Basically, isset() doesn't check for whether the variable is set at all, but whether it's set to anything but NULL. Given that, what's the best way to actually check for the existence of a variable? I tried something like: if(isset($v) || @is_null($v)) (the @ is necessary to avoid the warning when $v is not set) but is_null() has a similar problem to isset(): it returns TRUE on unset variables! It also appears that: @($v === NULL) works exactly like @is_null($v), so that's out, too. How are we supposed to reliably check for the existence of a variable in PHP? Edit: there is clearly a difference in PHP between variables that are not set, and variables that are set to NULL: <?php $a = array('b' => NULL); var_dump($a); PHP shows that $a['b'] exists, and has a NULL value. If you add: var_dump(isset($a['b'])); var_dump(isset($a['c'])); you can see the ambiguity I'm talking about with the isset() function. Here's the output of all three of these var_dump()s: array(1) { ["b"]=> NULL } bool(false) bool(false) Further edit: two things. One, a use case. An array being turned into the data of an SQL UPDATE statement, where the array's keys are the table's columns, and the array's values are the values to be applied to each column. Any of the table's columns can hold a NULL value, signified by passing a NULL value in the array. You need a way to differentiate between an array key not existing, and an array's value being set to NULL; that's the difference between not updating the column's value and updating the column's value to NULL. Second, Zoredache's answer, array_key_exists() works correctly, for my above use case and for any global variables: <?php $a = NULL; var_dump(array_key_exists('a', $GLOBALS)); var_dump(array_key_exists('b', $GLOBALS)); outputs: bool(true) bool(false) Since that properly handles just about everywhere I can see there being any ambiguity between variables that don't exist and variables that are set to NULL, I'm calling array_key_exists() the official easiest way in PHP to truly check for the existence of a variable. (Only other case I can think of is for class properties, for which there's property_exists(), which, according to its docs, works similarly to array_key_exists() in that it properly distinguishes between not being set and being set to NULL.)

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• How do I maximize a function in Mathematica which takes in a variable length list as input?

  - by Mike

  I have a time-series like function which gives an output based on a list of real numbers(i.e. you can run the function on a list of 1,2,3,... real numbers). The issue I'm encountering is how to maximize the function for a given list length(subject to a set of constraints). I could fix the function to a fixed number of real numbers(i.e. f [x_Real, y_Real] instead of f[x_List]) and treat x and y as the first two elements of the list, and call Maximize on the function, but this is not really elegant. I want to be able to easily change the number of elements in the list. What is the best way to optimize a function like I described, which takes a list as an argument, for a fixed list length?

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• help me with xor encryption in c#

  - by x86shadow

  I wrote this code in c# to encrypt a text with a key : using System; using System.Linq; using System.Collections.Generic; using System.Text; namespace ENCRYPT { class XORENC { private static int Bin2Dec(string num) { int _num = 0; for (int i = 0; i < num.Length; i++) { _num += (int)Math.Pow(2, num.Length - i - 1) * int.Parse(num[i].ToString()); } return _num; } private static string Dec2Bin(int num) { if (num < 2) return num.ToString(); return Dec2Bin(num / 2) + (num % 2).ToString(); } public static string StrXor(string str, string key) { string _str = ""; string _key = ""; string _dec = ""; string _temp = ""; for (int i = 0; i < str.Length; i++) { _temp = Dec2Bin(str[i]); for (int j = 0; j < 8 - _temp.Length + 1; j++) { _temp = '0' + _temp; } _str += _temp; } for (int i = 0; i < key.Length; i++) { _temp = Dec2Bin(key[i]); for (int j = 0; j < 8 - _temp.Length + 1; j++) { _temp = '0' + _temp; } _key += _temp; } while (_key.Length < _str.Length) { _key += _key; } if (_key.Length > _str.Length) _key = _key.Substring(0, _str.Length); for (int i = 0; i < _str.Length; i++) { if (_str[i] == _key[i]) { _dec += '0'; } else { _dec += '1'; } } _str = ""; for (int i = 0; i < _dec.Length; i = i + 8) { char _chr = (char)0; _chr = (char)Bin2Dec(_dec.Substring(i, 8)); _str += _chr; } return _str; } } } the problem is that I always get error when I want to decrypt an encryted text with this code. see the example below for more info : string enc_text = ENCRYPT.XORENC("abc","a"); //enc_text = " ??" string dec_text = ENCRYPT.XORENC(enc_text,"a"); //ERROR any one can help ?

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• need a recursive algorithm that determines whether there is a subset of a given length that adds up

  - by user311674

  this is similar to the subset sum problem but the subset has to be a certain length. need a recursive function

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• How to count the length (number of lines) of a csv file in Rails?

  - by Mathias

  Hello, I have a form (Rails) which allows me to load a .csv file using the file_field. In the view: <% form_for(:upcsv, :html => {:multipart => true}) do |f| %> <table> <tr> <td><%= f.label("File:") %></td> <td><%= f.file_field(:filename) %></td> </tr> </table> <%= f.submit("Submit") %> <% end %> Clicking Submit redirects me to another page (create.html.erb). The file was loaded fine, and I was able to read the contents just fine in this second page. I am trying to show the number of lines in the .csv file in this second page. My controller (semi-pseudocode): class UpcsvController < ApplicationController def index end def create file = params[:upcsv][:filename] ... #params[:upcsv][:file_length] = file.length # Show number of lines in the file #params[:upcsv][:file_length] = file.size ... end end Both file.length and file.size returns '91' when my file only contains 7 lines. From the Rails documentation that I read, once the Submit button is clicked, Rails creates a temp file of the uploaded file, and the params[:upcsv][:filename] contains the contents of the temp/uploaded file and not the path to the file. And I don't know how to extract the number of lines in my original file. What is the correct way to get the number of lines in the file? My create.html.erb: <table> <tr> <td>File length:</td> <td><%= params[:upcsv][:file_length] %></td> </tr> </table> I'm really new at Rails (just started last week), so please bear with my stupid questions. Thank you!

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• How to implement square root and exponentiation on arbitrary length numbers?

  - by tomp

  I'm working on new data type for arbitrary length numbers (only non-negative integers) and I got stuck at implementing square root and exponentiation functions (only for natural exponents). Please help. I store the arbitrary length number as a string, so all operations are made char by char. Please don't include advices to use different (existing) library or other way to store the number than string. It's meant to be a programming exercise, not a real-world application, so optimization and performance are not so necessary. If you include code in your answer, I would prefer it to be in either pseudo-code or in C++. The important thing is the algorithm, not the implementation itself. Thanks for the help.

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• How detect length of a numpy array with only one element?

  - by mishaF

  I am reading in a file using numpy.genfromtxt which brings in columns of both strings and numeric values. One thing I need to do is detect the length of the input. This is all fine provided there are more than one value read into each array. But...if there is only one element in the resulting array, the logic fails. I can recreate an example here: import numpy as np a = np.array(2.3) len(a) returns an error saying: TypeError: len() of unsized object however, If a has 2 or more elements, len() behaves as one would expect. import numpy as np a = np.array([2.3,3.6]) len(a) returns 2 My concern here is, if I use some strange exception handling, I can't distinguish between a being empty and a having length = 1.

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• How do I get the inner arrays length in a 2d array in C#?

  - by Phukab

  Lets say I create a jagged 2d array like so: public static char[,] phoneLetterMapping = { {'0'}, {'1'}, {'A', 'B', 'C'} }; Now, given the first index of the array, I would like to be able to get the length of the inner array. So, I would like to be able to do something like: phoneLetterMapping[2].length I can do that in Java. But the intellisense menu doesn't return the normal members of an array when I type in the first bracket of the [][] 2d array. So, how do I get the inner array lengths in my 2d array in C#?

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• Starting a SKProductsRequest gives -[_NSCFArray length] invalid selector error a moment later. LoadMicroPaymentsProductsOperation error.

  - by quantumpotato

  I'm fetching a list of identifiers from my server, then passing them off in a products request to Apple. Here's my code, and below is the error I'm getting. The iPhone 4 is not crashing when this happens. -(void)didReceiveData:(NSArray *)data { NSLog(@"Received Identifiers: %@",data); NSSet *productIdentifiers = [NSSet setWithArray:data]; SKProductsRequest *productsRequest = [[SKProductsRequest alloc] initWithProductIdentifiers:productIdentifiers]; productsRequest.delegate = self; [productsRequest start]; NSLog(@"productsRequest should have started by now"); } Wed Dec 29 09:42:14 iPhone XXXX-iphone[6363] <Warning>: Received Identifiers: ( ( 1, 10, "com.XXXX.XXXX.10" ) ) Wed Dec 29 09:42:14 iPhone XXXX-iphone[6363] <Warning>: productsRequest should have started by now Wed Dec 29 09:42:18 iPhone itunesstored[6367] : -[__NSCFArray length]: unrecognized selector sent to instance 0x119070 Wed Dec 29 09:42:18 iPhone itunesstored[6367] : caught -[__NSCFArray length]: unrecognized selector sent to instance 0x119070 exception with stack trace: (0x33ac0975 0x3347b49d 0x33ac2133 0x33a69aa9 0x33a69860 0x2717b 0x27515 0x31469651 0x314693ed 0x31469e39 0x3362795f 0x336276c3 0x3363c4eb 0x33c32680 0x33c32ba0 0x33bd7251 0x33bcf978)

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• how would you sort n sorted lists with average length K in O(n*log K) time?

  - by SS

  how would you sort n sorted lists with average length K in O(n*log K) time?

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• How to display values from another website to an new html page?

  - by user3098728

  How to display the value in a new html file from different website? This an example field of values that need to display into new html file and I want to display the said values in the input box (Contract ID) of this page JSFiddle. I have 2 JS code that would display that values, but unfortunately its not working and I dont know how to display that value in html input box. Please help me. Thank you I want to display the said value in this input box: Here the JS file to read the values: function scanLapVerification() { try { var page_title = "Title"; var el = getElement(document, "class", "view-operator-verification-title", ""); if (!el || el.length == 0) return; if (el[0].innerText != page_title) return; var page_title = ''; var el = getElement(document, "class", "workflowActivityDetailPanel", ""); if (el && el.length > 0) { var eltr = getElement(el[0], "tag", "tr", ""); if (eltr && eltr.length > 0) { //Read Contract ID var contractId = { CI: { id: null } }; var con_id = null; for (var i = 0; i < eltr.length; i++) { tr_text = eltr[i].innerText; if (tr_text.substr(0, "Contract ID".length) == "Contract ID") con_id = "CI"; if (con_id && tr_text.substr(0, "Contract ID".length) == "Contract ID") { contractId[con_id].id = tr_text.substr("Contract ID".length + 1, tr_text.length - "Contract ID".length - 1); } } var contract_id = contractId.CI.id; return { content: "cid_check", con_id: con_id }; } return { status: "KO" }; } catch (e) { alert("Exception: scanLapVerification\n" + e.Description); return { status: "KO", message: e }; } }; And here's the 2nd JS that display to a new html page: function scanLapVerification() { chrome.tabs.sendRequest(tabLapVerification, { method: "scanLapVerification" }, function (response) { msgbox("receiveResponse: scanLapVerification " + jsonToString(response, "JSON")); //maintaining state in the background if (response.data.content == "cid_check") { //Popup window features var popupWindow = null; var name; var width = 550; var height = 200; var left = parseInt((screen.availWidth / 2) - (width / 2)); var top = parseInt((screen.availHeight / 2) - (height / 2)); var windowFeatures = "width=" + width + ",height=" + height + ",left=" + left + ",top=" + top + "screenX=" + left + ",screenY=" + top; //Input new address with popup window if (confirm("Does the client has new address?") == true) { popupWindow = window.open('/htmlname.htm', "title", windowFeatures + encodeURIComponent(response.data.contract_id)); popupWindow.focus(); } else { name = ""; } }); }

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• Dynamic obstacles avoidance in navigation mesh system

  - by Variable

  I've built my path finding system with unreal engine, somehow the path finding part works just fine while i can't find a proper way to solve dynamic obstacles avoidance problem. My characters are walking allover the map and collide with each other while they moving. I try to steering them when collision occurs, but this doesn't work well. For example, two characters block on the road while the third one's path is right in the middle of them and he'll get stuck. Can someone tell me the most popular way of doing dynamic avoidance? Thanks a lot.

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• spliiting code in java-don't know what's wrong [closed]

  - by ???? ?????

  I'm writing a code to split a file into many files with a size specified in the code, and then it will join these parts later. The problem is with the joining code, it doesn't work and I can't figure what is wrong! This is my code: import java.io.*; import java.util.*; public class StupidSplit { static final int Chunk_Size = 10; static int size =0; public static void main(String[] args) throws IOException { String file = "b.txt"; int chunks = DivideFile(file); System.out.print((new File(file)).delete()); System.out.print(JoinFile(file, chunks)); } static boolean JoinFile(String fname, int nChunks) { /* * Joins the chunks together. Chunks have been divided using DivideFile * function so the last part of filename will ".partxxxx" Checks if all * parts are together by matching number of chunks found against * "nChunks", then joins the file otherwise throws an error. */ boolean successful = false; File currentDirectory = new File(System.getProperty("user.dir")); // File[] fileList = currentDirectory.listFiles(); /* populate only the files having extension like "partxxxx" */ List<File> lst = new ArrayList<File>(); // Arrays.sort(fileList); for (File file : fileList) { if (file.isFile()) { String fnm = file.getName(); int lastDot = fnm.lastIndexOf('.'); // add to list which match the name given by "fname" and have //"partxxxx" as extension" if (fnm.substring(0, lastDot).equalsIgnoreCase(fname) && (fnm.substring(lastDot + 1)).substring(0, 4).equals("part")) { lst.add(file); } } } /* * sort the list - it will be sorted by extension only because we have * ensured that list only contains those files that have "fname" and * "part" */ File[] files = (File[]) lst.toArray(new File[0]); Arrays.sort(files); System.out.println("size ="+files.length); System.out.println("hello"); /* Ensure that number of chunks match the length of array */ if (files.length == nChunks-1) { File ofile = new File(fname); FileOutputStream fos; FileInputStream fis; byte[] fileBytes; int bytesRead = 0; try { fos = new FileOutputStream(ofile,true); for (File file : files) { fis = new FileInputStream(file); fileBytes = new byte[(int) file.length()]; bytesRead = fis.read(fileBytes, 0, (int) file.length()); assert(bytesRead == fileBytes.length); assert(bytesRead == (int) file.length()); fos.write(fileBytes); fos.flush(); fileBytes = null; fis.close(); fis = null; } fos.close(); fos = null; } catch (FileNotFoundException fnfe) { System.out.println("Could not find file"); successful = false; return successful; } catch (IOException ioe) { System.out.println("Cannot write to disk"); successful = false; return successful; } /* ensure size of file matches the size given by server */ successful = (ofile.length() == StupidSplit.size) ? true : false; } else { successful = false; } return successful; } static int DivideFile(String fname) { File ifile = new File(fname); FileInputStream fis; String newName; FileOutputStream chunk; //int fileSize = (int) ifile.length(); double fileSize = (double) ifile.length(); //int nChunks = 0, read = 0, readLength = Chunk_Size; int nChunks = 0, read = 0, readLength = Chunk_Size; byte[] byteChunk; try { fis = new FileInputStream(ifile); StupidSplit.size = (int)ifile.length(); while (fileSize > 0) { if (fileSize <= Chunk_Size) { readLength = (int) fileSize; } byteChunk = new byte[readLength]; read = fis.read(byteChunk, 0, readLength); fileSize -= read; assert(read==byteChunk.length); nChunks++; //newName = fname + ".part" + Integer.toString(nChunks - 1); newName = String.format("%s.part%09d", fname, nChunks - 1); chunk = new FileOutputStream(new File(newName)); chunk.write(byteChunk); chunk.flush(); chunk.close(); byteChunk = null; chunk = null; } fis.close(); System.out.println(nChunks); // fis = null; } catch (FileNotFoundException fnfe) { System.out.println("Could not find the given file"); System.exit(-1); } catch (IOException ioe) { System.out .println("Error while creating file chunks. Exiting program"); System.exit(-1); }System.out.println(nChunks); return nChunks; } } }

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• Vector normalization gives very imprecise results

  - by Kipras

  When I normalize vectors I receive very strange results. The lengths of the normalized vectors range from 1.0 to almost 1.5. The functions are all written by me, but I just can't find a mistake in my algorithm. When I normalize I just divide all components of the vector by the vector's length. public double length(){ return Math.sqrt(x*x + y*y); } public void normalize(){ if(length() > 0){ x /= length(); y /= length(); } } Is this supposed to happen? I mean I can see the length ranging from 0.9 to 1.1 at worst, but this is just overwhelming. Cheers

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• Java curious Loop Performance

  - by user1680583

  I have a big problem while evaluate my java code. To simplify the problem I wrote the following code which produce the same curious behavior. Important is the method run() and given double value rate. For my runtime test (in the main method) I set the rate to 0.5 one times and 1.0 the other time. With the value 1.0 the if-statement will be executed in each loop iteration and with the value 0.5 the if-statement will be executed half as much. For this reason I expected longer runtime by the first case but opposite is true. Can anybody explain me this phenomenon?? The result of main: Test mit rate = 0.5 Length: 50000000, IF executions: 25000856 Execution time was 4329 ms. Length: 50000000, IF executions: 24999141 Execution time was 4307 ms. Length: 50000000, IF executions: 25001582 Execution time was 4223 ms. Length: 50000000, IF executions: 25000694 Execution time was 4328 ms. Length: 50000000, IF executions: 25004766 Execution time was 4346 ms. ================================= Test mit rate = 1.0 Length: 50000000, IF executions: 50000000 Execution time was 3482 ms. Length: 50000000, IF executions: 50000000 Execution time was 3572 ms. Length: 50000000, IF executions: 50000000 Execution time was 3529 ms. Length: 50000000, IF executions: 50000000 Execution time was 3479 ms. Length: 50000000, IF executions: 50000000 Execution time was 3473 ms. The Code public ArrayList<Byte> list = new ArrayList<Byte>(); public final int LENGTH = 50000000; public PerformanceTest(){ byte[]arr = new byte[LENGTH]; Random random = new Random(); random.nextBytes(arr); for(byte b : arr) list.add(b); } public void run(double rate){ byte b = 0; int count = 0; for (int i = 0; i < LENGTH; i++) { if(getRate(rate)){ list.set(i, b); count++; } } System.out.println("Length: " + LENGTH + ", IF executions: " + count); } public boolean getRate(double rate){ return Math.random() < rate; } public static void main(String[] args) throws InterruptedException { PerformanceTest test = new PerformanceTest(); long start, end; System.out.println("Test mit rate = 0.5"); for (int i = 0; i < 5; i++) { start=System.currentTimeMillis(); test.run(0.5); end = System.currentTimeMillis(); System.out.println("Execution time was "+(end-start)+" ms."); Thread.sleep(500); } System.out.println("================================="); System.out.println("Test mit rate = 1.0"); for (int i = 0; i < 5; i++) { start=System.currentTimeMillis(); test.run(1.0); end = System.currentTimeMillis(); System.out.println("Execution time was "+(end-start)+" ms."); Thread.sleep(500); } }

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• Does a high run queue length average result in poor performance for a web server?

  - by Domino

  I'm trying to narrow down the list of suspects of web servers that perform moderately well most of the time with occasional bouts of poor performance. I'm analyzing the data collected and summarized by sar. I've noticed a few things, one of which is high number of tasks in the run queue. 10:15:01 AM runq-sz plist-sz ldavg-1 ldavg-5 ldavg-15 blocked 10:25:01 AM 2 150 0.05 0.05 0.06 0 10:35:01 AM 4 149 0.08 0.12 0.09 0 10:45:01 AM 6 150 0.13 0.19 0.15 0 10:55:01 AM 1 150 0.08 0.10 0.13 0 11:05:01 AM 4 150 0.20 0.35 0.23 0 11:15:01 AM 3 149 0.02 0.09 0.15 0 11:25:01 AM 7 149 0.04 0.05 0.11 0 11:35:01 AM 4 150 0.14 0.15 0.13 0 11:45:01 AM 6 150 0.27 0.18 0.16 0 11:55:01 AM 5 150 0.08 0.10 0.13 0 12:05:01 PM 3 149 0.35 0.40 0.26 0 12:15:01 PM 19 155 0.02 0.10 0.16 1 12:25:01 PM 2 150 0.00 0.07 0.12 0 12:35:02 PM 3 151 0.58 0.24 0.17 0 12:45:01 PM 8 150 0.02 0.13 0.15 0 12:55:01 PM 6 149 0.81 0.29 0.18 0 01:05:01 PM 3 148 0.00 0.09 0.13 0 01:15:01 PM 7 149 0.00 0.04 0.11 0 I believe these are 10 minute averages. Is this an indicator that the web server is not performing as fast as it could if the average run queue length was lower?

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• Is it possible to use ffmpeg to trim off X seconds from the beginning of a video with an unspecified length?

  - by marcelebrate

  I need to trim the just the first 1 or 2 seconds off of a series of FLV recordings of varying, unspecified lengths. I've found plenty of resources for extracting a specified duration from a video (e.g. 30 second clips), but none for continuing to the end of a video. Both of these attempts just yield a copied version of the video, sans desired trimming: ffmpeg -ss 2 -vcodec copy -acodec copy -i input.flv output.flv ffmpeg -ss 2 -t 120 -vcodec copy -acodec copy -i input.flv output.flv The thought on the second one was: perhaps if I specified a length beyond what was possible, it'd just go to the end. No dice. I know it's not an issue with codecs or using seconds instead of timecode since the following worked a charm: ffmpeg -ss 2 -t 5 -vcodec copy -acodec copy -i input.flv output.flv Any other ideas? I'm open to using other (Windows-based) command line tools, however am strongly favoring ffmpeg since I'm already using it for thumbnail creation and am familiar with it. If it helps, my videos will all be under 2 minutes.

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• Getting a variable into another class through properties or button tags with Iphone SDK?

  - by MarcZero

  Hello. I have been pounding my head against a wall trying to figure out what I think is a simple thing to do, but I have, so far, been unable to figure it out with the iPhone SDK. I have a view with 4 buttons. When I push the buttons, I have another view called and come up to take over the screen. I want to have a simple variable passed from the old view to the new view. The purpose of this is to know what button was pressed out of the four identical ones. (trying to get an int value of 1 through 4) Here is what I have tried so far: I initially tried to call the variable from the class itself. My understanding was that my new view was only sitting on top of the old view, so it should not have been released. I could not get access to the variable as the variable was said to not be declared. I then tried to create a method that would return the int value. Again, the view class was not seen and was being declared as a "first use" of it. I then attempted to follow another similar post on here that suggested to try and send the button tag number to some part of the new view. I attempted to do this by setting the new views button title but I still cannot figure out a way to code it without coming up with errors. I am just looking for what method would be the best for me to pursue. I have no problem going back and reading the books on Objective-C, but I'm just trying to figure out which way I should concentrate on. Thank you for any insight.

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• How do you set a variable to be an empty, but workable Jquery object?

  - by KallDrexx

  Outside of a for I declare a variable using var list;. I use this variable inside of my for loop like so: // add the html to the list if (list == undefined) list = item; else list.append(item.contents()); item is a cloned jquery object build from a $('list_template').clone(); call (list_template is a div with <li> elements inside). What I am doing is creating a list, which I will then appendTo() where I need it. Right now this code works fine, but it doesn't seem right to me. Unfortunatly, I cannot seem to figure out how to correctly declare the list variable to be an empty Jquery object. I have tried both: var list = $([]); var list = $(''); Both of those cause the append to not work correctly (or as expected) with list.html() being null. Is there a way to initialize my variable to an empty jquery object, so all I have to do is list.append(item.contents()); without the if/else statements?

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• In ArrayBlockingQueue, why copy into ReentrantLock field into local final variable?

  - by mjlee

  In ArrayBlockingQueue, any method that requires lock will get set 'final' local variable before calling 'lock()'. public boolean offer(E e) { if (e == null) throw new NullPointerException(); final ReentrantLock lock = this.lock; lock.lock(); try { if (count == items.length) return false; else { insert(e); return true; } } finally { lock.unlock(); } } Is there any reason to set a local variable 'lock' from 'this.lock' when field 'this.lock' is final also. Additionally, it also set local variable of E[] before acting on. private E extract() { final E[] items = this.items; E x = items[takeIndex]; items[takeIndex] = null; takeIndex = inc(takeIndex); --count; notFull.signal(); return x; } Is there any reason for copying to local final variable?

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• Create a variable which is named depending on an ID number?

  - by gray

  Is there any way to create a variable, and add an ID to the end of the actual variable name? I have a variable called 'gauge', used to create a new Gauge object: var gauge = new Gauge(target).setOptions(opts); I want to add an ID to the variable, so something like: var gauge+id = new Gauge(target).setOptions(opts); It's because I'm creating a number of these objects, and have a specific ID already for each one, which I want to attach to the gauge object if possible? All my code for this function is below, if it gives you a better idea of what i need to do: function go(id, votes) { var val = $('#votes_'+id).text(); var target = document.getElementById('foo_'+id); // your canvas element var gauge = new Gauge(target).setOptions(opts); // create sexy gauge! gauge.maxValue = 100; // set max gauge value gauge.animationSpeed = 20; // set animation speed (32 is default value) var a=votes+0.5; gauge.set(val); // set actual value } My main problem arises on the last line. It says gauge.set(val), and it only sets the last object, ignoring all the other ones...

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• Wouldn't it be nice to have a type variable referring to the class's instance.

  - by user93197

  I often have a pattern like this: class VectorBase<SubClass, Element> where SubClass : VectorBase<SubClass, Element>, new() where Element : Addable<Element> { Element[] data; public VectorBase(Element[] data) { this.data = data; } public SubClass add(SubClass second) { Element[] newData = new Element[data.Length]; for (int i = 0; i < newData.Length; i++) { newData[i] = data[i].add(second.data[i]); } SubClass result = new SubClass(); result.data = newData; return result; } } class VectorInt : VectorBase<VectorInt, Int32> { } class MyInt : Addable<MyInt> { int data; public MyInt(int data) { this.data = data; } public MyInt add(MyInt t) { return new MyInt(data + t.data); } } interface Addable<T> { T add(T t); } But I would rather just have: class VectorBase2<Element> where Element : Addable<Element> { Element[] data; public VectorBase(Element[] data) { this.data = data; } public SubClass add(SubClass second) { Element[] newData = new Element[data.Length]; for (int i = 0; i < newData.Length; i++) { newData[i] = data[i].add(second.data[i]); } SubClass result = new SubClass(data); return result; } } class VectorInt2 : VectorBase2<Int32> { } Why not make the subclass type available to all classes? Is this technically impossible?

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• In ArrayBlockingQueue, why copy final member field into local final variable?

  - by mjlee

  In ArrayBlockingQueue, any method that requires lock will get set 'final' local variable before calling 'lock()'. public boolean offer(E e) { if (e == null) throw new NullPointerException(); final ReentrantLock lock = this.lock; lock.lock(); try { if (count == items.length) return false; else { insert(e); return true; } } finally { lock.unlock(); } } Is there any reason to set a local variable 'lock' from 'this.lock' when field 'this.lock' is final also. Additionally, it also set local variable of E[] before acting on. private E extract() { final E[] items = this.items; E x = items[takeIndex]; items[takeIndex] = null; takeIndex = inc(takeIndex); --count; notFull.signal(); return x; } Is there any reason for copying to local final variable?

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