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POHow can I determine if an element exists in an array (perl)
 

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  1. POHow can I determine if an element exists in an array (perl)
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    <p>I'm looping through an array, and I want to test if an element is found in another array.</p> <p>In pseudo-code, what I'm trying to do is this:</p> <pre><code>foreach $term (@array1) { if ($term is found in @array2) { #do something here } } </code></pre> <p>I've got the "foreach" and the "do something here" parts down-pat ... but everything I've tried for the "if term is found in array" test does NOT work ...</p> <p>I've tried grep: </p> <pre><code>if grep {/$term/} @array2 { #do something } # this test always succeeds for values of $term that ARE NOT in @array2 if (grep(/$term/, @array2)) { #do something } # this test likewise succeeds for values NOT IN the array </code></pre> <p>I've tried a couple different flavors of "converting the array to a hash" which many previous posts have indicated are so simple and easy ... and none of them have worked.</p> <p>I am a long-time low-level user of perl, I understand just the basics of perl, do not understand all the fancy obfuscated code that comprises 99% of the solutions I read on the interwebs ... I would really, truly, honestly appreciate any answers that are explicit in the code and provide a step-by-step explanation of what the code is doing ... </p> <p>... I seriously don't grok $_ and any other kind or type of hidden, understood, or implied value, variable, or function. I would really appreciate it if any examples or samples have all variables and functions named with clear terms ($term as opposed to $_) ... and describe with comments what the code is doing so I, in all my mentally deficient glory, may hope to possibly understand it some day. Please. :-)</p> <p>...</p> <p>I have an existing script which uses 'grep' somewhat succesfully:</p> <pre><code>$rc=grep(/$term/, @array); if ($rc eq 0) { #something happens here } </code></pre> <p>but I applied that EXACT same code to my new script and it simply does NOT succeed properly ... i.e., it "succeeds" (rc = zero) when it tests a value of $term that I know is NOT present in the array being tested. I just don't get it.</p> <p>The ONLY difference in my 'grep' approach between 'old' script and 'new' script is how I built the array ... in old script, I built array by reading in from a file:</p> <pre><code> @array=`cat file`; </code></pre> <p>whereas in new script I put the array inside the script itself (coz it's small) ... like this:</p> <pre><code> @array=("element1","element2","element3","element4"); </code></pre> <p>How can that result in different output of the grep function? They're both bog-standard arrays! I don't get it!!!! :-(</p> ######################################################################## <h3>addendum ... some clarifications or examples of my actual code:</h3> ######################################################################## <p>The term I'm trying to match/find/grep is a word element, for example "word123". </p> <p>This exercise was just intended to be a quick-n-dirty script to find some important info from a file full of junk, so I skip all the niceties (use strict, warnings, modules, subroutines) by choice ... this doesn't have to be elegant, just simple. </p> <p>The term I'm searching for is stored in a variable which is instantiated via split:</p> <pre><code>foreach $line(@array1) { chomp($line); # habit # every line has multiple elements that I want to capture ($term1,$term2,$term3,$term4)=split(/\t/,$line); # if a particular one of those terms is found in my other array 'array2' if (grep(/$term2/, @array2) { # then I'm storing a different element from the line into a 3rd array which eventually will be outputted push(@known, $term1) unless $seen{$term1}++; } } </code></pre> <p>see that grep up there? It ain't workin right ... it is succeeding for all values of $term2 even if it is definitely NOT in array2 ... array1 is a file of a couple thousand lines. The element I'm calling $term2 here is a discrete term that may be in multiple lines, but is never repeated (or part of a larger string) within any given line. Array2 is about a couple dozen elements that I need to "filter in" for my output. </p> <p>... </p> <p>I just tried one of the below suggestions: </p> <pre><code>if (grep $_ eq $term2, @array2) </code></pre> <p>And this grep failed for all values of $term2 ... I'm getting an all or nothing response from grep ... so I guess I need to stop using grep. Try one of those hash solutions ... but I really could use more explanation and clarification on those.</p>
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    1. COCan you provide a short script (on pastebin or equivalent) that recreates your problem? That would help us diagnose what's going on.
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      1. USDancrumb
    2. CO[How can I tell whether a certain element is contained in a list or array?](http://perldoc.perl.org/perlfaq4.html#How-can-I-tell-whether-a-certain-element-is-contained-in-a-list-or-array?)
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    3. COhttp://stackoverflow.com/questions/2860226/how-can-i-check-if-a-perl-array-contains-a-particular-value
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      1. USmatthias krull
 

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