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  • Hash Map Usage and Idea

    - by Anand
    Hi, I have been working in Java for the last 6 months and have been using Hash Maps What is the basic idea of a Hash Map ? I am using it as it easy for me to store so much data with direct key references rather than having to iterate through an arraylist ? Where is the power of Hash Map seen ? What is the scientific idea behind this data structure ?

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  • good __eq__, __lt__, ..., __hash__ methods for image class?

    - by Marten Bauer
    I create the following class: class Image(object): def __init__(self, extension, data, urls=None, user_data=None): self._extension = extension self._data = data self._urls = urls self._user_data = user_data self._hex_digest = hashlib.sha1(self._data).hexDigest() Images should be equal when all values are equal. Therefore I wrote: def __eq__(self, other): if isinstance(other, Image) and self.__dict__ == other.__dict__: return True return False def __ne__(self, other): return not self.__eq__(other) def __lt__(self, other): return self.__dict__ < other.__dict__ ... But how should the __hash__ method look like? Equal Images should return equal hashes... def __hash__(self): # won't work !?! return hash(self.__dict__) Is the way I try to use __eq__, __ne__, __lt__, __hash__, ... recommend?

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  • Turning a nested hash structure into a non-nested hash structure - is this the cleanest way to do it

    - by knorv
    Assume a nested hash structure %old_hash .. my %old_hash; $old_hash{"foo"}{"bar"}{"zonk"} = "hello"; .. which we want to "flatten" (sorry if that's the wrong terminology!) to a non-nested hash using the sub &flatten(...) so that .. my %h = &flatten(\%old_hash); die unless($h{"zonk"} eq "hello"); The following definition of &flatten(...) does the trick: sub flatten { my $hashref = shift; my %hash; my %i = %{$hashref}; foreach my $ii (keys(%i)) { my %j = %{$i{$ii}}; foreach my $jj (keys(%j)) { my %k = %{$j{$jj}}; foreach my $kk (keys(%k)) { my $value = $k{$kk}; $hash{$kk} = $value; } } } return %hash; } While the code given works it is not very readable or clean. My question is two-fold: In what ways does the given code not correspond to modern Perl best practices? Be harsh! :-) How would you clean it up?

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  • Sort by values from hash table - Ruby

    - by Adnan
    Hello, I have the following hash of countries; COUNTRIES = { 'Albania' => 'AL', 'Austria' => 'AT', 'Belgium' => 'BE', 'Bulgaria' => 'BG', ..... } Now when I output the hash the values are not ordered alphabetically AL, AT, BE, BG ....but rather in a nonsense order (at least for me) How can I output the hash having the values ordered alphabetically?

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  • [Haskell]Curious about the Hash Table problem

    - by astamatto
    I read that hash tables in haskell are crippled ( citation: http://flyingfrogblog.blogspot.com/2009/04/more-on-haskells-hash-table-problems.html ) and since i like haskell it worried me. Since the blog-post one year has passed and im curious, The hash table problem in haskell was "fixed" in the traditional compilers? (like ghc) ps: I love stack overflow, im a long time visitor but only today i decided to try to post a question.

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  • Cleaning up code - flatten a nested hash structure

    - by knorv
    The following Perl sub flattens a nested hash structure: sub flatten { my $hashref = shift; my %hash; my %i = %{$hashref}; foreach my $ii (keys(%i)) { my %j = %{$i{$ii}}; foreach my $jj (keys(%j)) { my %k = %{$j{$jj}}; foreach my $kk (keys(%k)) { my $value = $k{$kk}; $hash{$kk} = $value; } } } return %hash; } While the code works it is not very readable or clean. My question is two-fold: In what ways does it not correspond to modern Perl best practices? How would you clean it up?

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  • Combine hash values in C#

    - by Chris
    I'm creating a generic object collection class and need to implement a Hash function. I can obviously (and easily!) get the hash values for each object but was looking for the 'correct' way to combine them to avoid any issues. Does just adding, xoring or any basic operation harm the quality of the hash or am I going to have to do something like getting the objects as bytes, combining them and then hashing that? Cheers in advance

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  • How can I marshal a hash with arrays?

    - by tuner
    What should I do to marshal an hash of arrays? The following code only prints {}. s = Hash.new s.default = Array.new s[0] << "Tigger" s[7] << "Ruth" s[7] << "Puuh" data = Marshal.dump(s) ls = Marshal.restore( data ) p ls If the hash doesn't contain an array it is restored properly.

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  • Hash value in the manifest file.

    - by satishtech
    Hello, Im tring to create a manifest for my own.dll, i took the manifest file from C:\WINDOWS\WinSxS\Manifests for example. In that, below tag was one of the line.<file name="msvcr90.dll" hashalg="SHA1" hash="e0dcdcbfcb452747da530fae6b000d47c8674671"> In above tag, hash value was assigned with 40 character. Here comes my doubt, 1) hash value was auto generated, if not, whats it points to?

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  • How do I access a value of a nested Perl hash?

    - by st
    I am new to Perl and I have a problem that's very simple but I cannot find the answer when consulting my Perl book. When printing the result of Dumper($request); I get the following result: $VAR1 = bless( { '_protocol' => 'HTTP/1.1', '_content' => '', '_uri' => bless( do{\(my $o = 'http://myawesomeserver.org:8081/counter/')}, 'URI::http' ), '_headers' => bless( { 'user-agent' => 'Mozilla/5.0 (X11; U; Linux i686; en; rv:1.9.0.4) Gecko/20080528 Epiphany/2.22 Firefox/3.0', 'connection' => 'keep-alive', 'cache-control' => 'max-age=0', 'keep-alive' => '300', 'accept' => 'text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8', 'accept-language' => 'en-us,en;q=0.5', 'accept-encoding' => 'gzip,deflate', 'host' => 'localhost:8081', 'accept-charset' => 'ISO-8859-1,utf-8;q=0.7,*;q=0.7' }, 'HTTP::Headers' ), '_method' => 'GET', '_handle' => bless( \*Symbol::GEN0, 'FileHandle' ) }, 'HTTP::Server::Simple::Dispatched::Request' ); How can I access the values of '_method' ('GET') or of 'host' ('localhost:8081'). I know that's an easy question, but Perl is somewhat cryptic at the beginning.

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  • Collision free hash function for a specific data structure

    - by Max
    Is it possible to create collision free hash function for a data structure with specific properties. The datastructure is int[][][] It contains no duplicates The range of integers that are contained in it is defined. Let's say it's 0..1000, the maximal integer is definitely not greater than 10000. Big problem is that this hash function should also be very fast. Is there a way to create such a hash function? Maybe at run time depending on the integer range?

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  • in ruby, how do you make this nested hash work?

    - by David
    this one creates an error: @settings = { :tab1 => { :name => { :required => true }, :description } } need to change :descrpition to :description = {}, but i don't have any values for :description so i want it to remain as is (without the empty = {}) Would you show me the best way to handle this kind of situation? thanks in advance

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  • How can I merge several hashes into one hash in Perl?

    - by Nick
    In Perl, how do I get this: $VAR1 = { '999' => { '998' => [ '908', '906', '0', '998', '907' ] } }; $VAR1 = { '999' => { '991' => [ '913', '920', '918', '998', '916', '919', '917', '915', '912', '914' ] } }; $VAR1 = { '999' => { '996' => [] } }; $VAR1 = { '999' => { '995' => [] } }; $VAR1 = { '999' => { '994' => [] } }; $VAR1 = { '999' => { '993' => [] } }; $VAR1 = { '999' => { '997' => [ '986', '987', '990', '984', '989', '988' ] } }; $VAR1 = { '995' => { '101' => [] } }; $VAR1 = { '995' => { '102' => [] } }; $VAR1 = { '995' => { '103' => [] } }; $VAR1 = { '995' => { '104' => [] } }; $VAR1 = { '995' => { '105' => [] } }; $VAR1 = { '995' => { '106' => [] } }; $VAR1 = { '995' => { '107' => [] } }; $VAR1 = { '994' => { '910' => [] } }; $VAR1 = { '993' => { '909' => [] } }; $VAR1 = { '993' => { '904' => [] } }; $VAR1 = { '994' => { '985' => [] } }; $VAR1 = { '994' => { '983' => [] } }; $VAR1 = { '993' => { '902' => [] } }; $VAR1 = { '999' => { '992' => [ '905' ] } }; to this: $VAR1 = { '999:' => [ { '992' => [ '905' ] }, { '993' => [ { '909' => [] }, { '904' => [] }, { '902' => [] } ] }, { '994' => [ { '910' => [] }, { '985' => [] }, { '983' => [] } ] }, { '995' => [ { '101' => [] }, { '102' => [] }, { '103' => [] }, { '104' => [] }, { '105' => [] }, { '106' => [] }, { '107' => [] } ] }, { '996' => [] }, { '997' => [ '986', '987', '990', '984', '989', '988' ] }, { '998' => [ '908', '906', '0', '998', '907' ] }, { '991' => [ '913', '920', '918', '998', '916', '919', '917', '915', '912', '914' ] } ]};

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  • Calculate sum of objects for each unique object property in Ruby

    - by macek
    I was helping with an answer in this question and it sparked a question of my own. Pie is an object that has a pieces array made of of PiePiece objects. Each PiePiece has a flavor attribute How do I create a hash that looks like this: # flavor => number of pieces { :cherry => 3 :apple => 1 :strawberry => 2 } This works, but I think it could be improved def inventory hash = {} pieces.each do |p| hash[p.flavor] ||= 0 hash[p.flavor] += 1 end hash end Any ideas?

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  • T-SQL - Left Outer Joins - Fileters in the where clause versus the on clause.

    - by Greg Potter
    I am trying to compare two tables to find rows in each table that is not in the other. Table 1 has a groupby column to create 2 sets of data within table one. groupby number ----------- ----------- 1 1 1 2 2 1 2 2 2 4 Table 2 has only one column. number ----------- 1 3 4 So Table 1 has the values 1,2,4 in group 2 and Table 2 has the values 1,3,4. I expect the following result when joining for Group 2: `Table 1 LEFT OUTER Join Table 2` T1_Groupby T1_Number T2_Number ----------- ----------- ----------- 2 2 NULL `Table 2 LEFT OUTER Join Table 1` T1_Groupby T1_Number T2_Number ----------- ----------- ----------- NULL NULL 3 The only way I can get this to work is if I put a where clause for the first join: PRINT 'Table 1 LEFT OUTER Join Table 2, with WHERE clause' select table1.groupby as [T1_Groupby], table1.number as [T1_Number], table2.number as [T2_Number] from table1 LEFT OUTER join table2 --****************************** on table1.number = table2.number --****************************** WHERE table1.groupby = 2 AND table2.number IS NULL and a filter in the ON for the second: PRINT 'Table 2 LEFT OUTER Join Table 1, with ON clause' select table1.groupby as [T1_Groupby], table1.number as [T1_Number], table2.number as [T2_Number] from table2 LEFT OUTER join table1 --****************************** on table2.number = table1.number AND table1.groupby = 2 --****************************** WHERE table1.number IS NULL Can anyone come up with a way of not using the filter in the on clause but in the where clause? The context of this is I have a staging area in a database and I want to identify new records and records that have been deleted. The groupby field is the equivalent of a batchid for an extract and I am comparing the latest extract in a temp table to a the batch from yesterday stored in a partioneds table, which also has all the previously extracted batches as well. Code to create table 1 and 2: create table table1 (number int, groupby int) create table table2 (number int) insert into table1 (number, groupby) values (1, 1) insert into table1 (number, groupby) values (2, 1) insert into table1 (number, groupby) values (1, 2) insert into table2 (number) values (1) insert into table1 (number, groupby) values (2, 2) insert into table2 (number) values (3) insert into table1 (number, groupby) values (4, 2) insert into table2 (number) values (4)

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  • SQL different joins not making any difference to result

    - by Chrissi
    I'm trying to write a quick (ha!) program to organise some of my financial information. What I ideally want is a query that will return all records with financial information in them from TableA. There should be one row for each month, but in instances where there were no transactions for a month there will be no record. I get results like this: SELECT Period,Year,TotalValue FROM TableA WHERE Year='1997' Result: Period Year TotalValue 1 1997 298.16 2 1997 435.25 4 1997 338.37 8 1997 336.07 9 1997 578.97 11 1997 361.23 By joining on a table (well a View in this instance) which just contains a field Period with values from 1 to 12, I expect to get something like this: SELECT p.Period,a.Year,a.TotalValue FROM Periods AS p LEFT JOIN TableA AS a ON p.Period = a.Period WHERE Year='1997' Result: Period Year TotalValue 1 1997 298.16 2 1997 435.25 3 NULL NULL 4 1997 338.37 5 NULL NULL 6 NULL NULL 7 NULL NULL 8 1997 336.07 9 1997 578.97 10 NULL NULL 11 1997 361.23 12 NULL NULL What I'm actually getting though is the same result no matter how I join it (except CROSS JOIN which goes nuts, but it's really not what I wanted anyway, it was just to see if different joins are even doing anything). LEFT JOIN, RIGHT JOIN, INNER JOIN all fail to provide the NULL records I am expecting. Is there something obvious that I'm doing wrong in the JOIN? Does it matter that I'm joining onto a View?

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  • Using the JPA Criteria API, can you do a fetch join that results in only one join?

    - by Shaun
    Using JPA 2.0. It seems that by default (no explicit fetch), @OneToOne(fetch = FetchType.EAGER) fields are fetched in 1 + N queries, where N is the number of results containing an Entity that defines the relationship to a distinct related entity. Using the Criteria API, I might try to avoid that as follows: CriteriaBuilder builder = entityManager.getCriteriaBuilder(); CriteriaQuery<MyEntity> query = builder.createQuery(MyEntity.class); Root<MyEntity> root = query.from(MyEntity.class); Join<MyEntity, RelatedEntity> join = root.join("relatedEntity"); root.fetch("relatedEntity"); query.select(root).where(builder.equals(join.get("id"), 3)); The above should ideally be equivalent to the following: SELECT m FROM MyEntity m JOIN FETCH myEntity.relatedEntity r WHERE r.id = 3 However, the criteria query results in the root table needlessly being joined to the related entity table twice; once for the fetch, and once for the where predicate. The resulting SQL looks something like this: SELECT myentity.id, myentity.attribute, relatedentity2.id, relatedentity2.attribute FROM my_entity myentity INNER JOIN related_entity relatedentity1 ON myentity.related_id = relatedentity1.id INNER JOIN related_entity relatedentity2 ON myentity.related_id = relatedentity2.id WHERE relatedentity1.id = 3 Alas, if I only do the fetch, then I don't have an expression to use in the where clause. Am I missing something, or is this a limitation of the Criteria API? If it's the latter, is this being remedied in JPA 2.1 or are there any vendor-specific enhancements? Otherwise, it seems better to just give up compile-time type checking (I realize my example doesn't use the metamodel) and use dynamic JPQL TypedQueries.

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  • Join our webcast: Discover What’s New in Oracle Data Integrator and Oracle GoldenGate

    - by Irem Radzik
    Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman","serif"; mso-fareast-font-family:"Times New Roman";} Data integration team has organized a series of webcasts for this summer. We are kicking it off this Thursday June 30th at 10am PT with a product update webcast: Discover What’s New in Oracle Data Integrator and Oracle GoldenGate. In this webcast you will hear from product management about the new patch updates to both GoldenGate 11g R1 and ODI 11gR1. Jeff Pollock, Sr. Director of Product Management for ODI will talk about the new features in Oracle Data Integrator 11.1.1.5, including the data lineage integration with OBI EE, enhanced web services to support flexible architectures as well as capabilities for efficient object execution such as Load Plans. Jeff will discuss support for complex files and performance enhancements. Chris McAllister, Sr. Director of Product Management for Oracle GoldenGate will cover the new features of Oracle GoldenGate 11.1.1.1 such as increased data security by supporting Oracle Database Advanced Security option, deeper integration with Oracle Database, and the expanded list of heterogeneous databases GoldenGate supports . Chris will also talk about the new Oracle GoldenGate 11gR1 release for HP NonStop platform and will provide information on our strategic direction for product development. Join us this Thursday at 10am PT/ 1pm ET to hear directly from Data Integration Product Management . You can register here for the June 30th webcast as well as for the upcoming ones in our summer webcast series.

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  • Join us for Live Oracle VM and Oracle Linux Cloud Events in Europe

    - by Monica Kumar
    Join us for a series of live events and discover how Oracle VM and Oracle Linux offer an integrated and optimized infrastructure for quickly deploying a private cloud environment at lower cost. As one of the most widely deployed operating systems today, Oracle Linux delivers higher performance, better reliability, and stability, at a lower cost for your cloud environments. Oracle VM is an application-driven server virtualization solution fully integrated and certified with Oracle applications to deliver rapid application deployment and simplified management. With Oracle VM, you have peace of mind that the entire Oracle stack deployed is fully certified by Oracle. Register now for any of the upcoming events, and meet with Oracle experts to discuss how we can help in enabling your private cloud. Nov 20: Foundation for the Cloud: Oracle Linux and Oracle VM (Belgium) Nov 21: Oracle Linux & Oracle VM Enabling Private Cloud (Germany) Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 Nov 28: Realize Substantial Savings and Increased Efficiency with Oracle Linux and Oracle VM (Luxembourg) Nov 29: Foundation for the Cloud: Oracle Linux and Oracle VM (Netherlands)Dec 5: MySQL Tech Tour, including Oracle Linux and Oracle VM (France) Hope to see you at one of these events!

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