I am new in Perl programming. I am trying to compare the two arrays each element. So here is my code:
#!/usr/bin/perl
use strict;
use warnings;
use v5.10.1;
my #x = ("tom","john","michell");
my #y = ("tom","john","michell","robert","ricky");
if (#x ~~ #y)
{
say "elements matched";
}
else
{
say "no elements matched";
}
When I run this I get the output
no elements matched
So I want to compare both array elements in deep and the element do not matches, those elements I want to store it in a new array. As I can now compare the only matched elements but I can't store it in a new array.
How can I store those unmatched elements in a new array?
Please someone can help me and advice.
I'd avoid smart matching in Perl - e.g. see here
If you're trying to compare the contents of $y[0] with $x[0] then this is one way to go, which puts all non-matches in an new array #keep:
use strict;
use warnings;
use feature qw/say/;
my #x = qw(tom john michell);
my #y = qw(tom john michell robert ricky);
my #keep;
for (my $i = 0; $i <$#y; $i++) {
unless ($y[$i] eq $x[$i]){
push #keep, $y[$i];
}
}
say for #keep;
Or, if you simply want to see if one name exists in the other array (and aren't interested in directly comparing elements), use two hashes:
my (%x, %y);
$x{$_}++ for #x;
$y{$_}++ for #y;
foreach (keys %y){
say if not exists $x{$_};
}
It would be well worth your while spending some time reading the Perl FAQ.
Perl FAQ 4 concerns Data Manipulation and includes the following question and answer:
How do I compute the difference of two arrays? How do I compute
the intersection of two arrays?
Use a hash. Here's code to do both and more. It assumes that each
element is unique in a given array:
my (#union, #intersection, #difference);
my %count = ();
foreach my $element (#array1, #array2) { $count{$element}++ }
foreach my $element (keys %count) {
push #union, $element;
push #{ $count{$element} > 1 ? \#intersection : \#difference }, $element;
}
Note that this is the symmetric difference, that is, all elements
in either A or in B but not in both. Think of it as an xor
operation.
Related
I have a array which have certain elements. Each element have two char "BC" followed by a number
e.g - "BC6"
I want to extract the number which is present and store in a different array.
use strict;
use warnings;
use Scalar::Util qw(looks_like_number);
my #band = ("BC1", "BC3");
foreach my $elem(#band)
{
my #chars = split("", $elem);
foreach my $ele (#chars) {
looks_like_number($ele) ? 'push #band_array, $ele' : '';
}
}
After execution #band_array should contain (1,3)
Can someone please tell what I'm doing wrong? I am new to perl and still learning
To do this with a regular expression, you need a very simple pattern. /BC(\d)/ should be enough. The BC is literal. The () are a capture group. They save the match inside into a variable. The first group relates to $1 in Perl. The \d is a character group for digits. That's 0-9 (and others, but that's not relevant here).
In your program, it would look like this.
use strict;
use warnings;
use Data::Dumper;
my #band = ('BC1', 'BC2');
my #numbers;
foreach my $elem (#band) {
if ($elem =~ m/BC(\d)/) {
push #numbers, $1;
}
}
print Dumper #numbers;
This program prints:
$VAR1 = '1';
$VAR2 = '2';
Note that your code had several syntax errors. The main one is that you were using #band = [ ... ], which gives you an array that contains one array reference. But your program assumed there were strings in that array.
Just incase your naming contains characters other than BC this will exctract all numeric values from your list.
use strict;
use warnings;
my #band = ("AB1", "BC2", "CD3");
foreach my $str(#band) {
$str =~ s/[^0-9]//g;
print $str;
}
First, your array is an anonymous array reference; use () for a regular array.
Then, i would use grep to filter out the values into a new array
use strict;
use warnings;
my #band = ("BC1", "BC3");
my #band_array = grep {s/BC(\d+)/$1/} #band;
$"=" , "; # make printing of array nicer
print "#band_array\n"; # print array
grep works by passing each element of an array in the code in { } , just like a sub routine. $_ for each value in the array is passed. If the code returns true then the value of $_ after the passing placed in the new array.
In this case the s/// regex returns true if a substitution is made e.g., the regex must match. Here is link for more info on grep
I have a several files that have contain product install information.
I am able to grep for the elements that I want (for example, "version") from the files. And I end up with something like this:
instancefile1:ABC_version=1.2.3
instancefile1:XYZ_version=2.5
instancefile2:ABC_version=3.4.5
instancefile3:XYZ_version=1.1
Where the components are named ABC or XYZ.
What I'd like to do is take this grep output and parse it through perl to build arrays on the file.
The first array would be composed of the instance number (pulled from the filenames) - above, I'd have an array that would have 1,2,3 as elements.
And inside each of those arrays would be the components that that particular instance has.
Full expected arrays and components from above:
array[0] = instancefile1 # can keep this named like the filename,
or assign name. Does not matter
array[0][0] = ABC_version=1.2.3
array[0][1] = XYZ_version=2.5
array[1] = instancefile2
array[1][0] = ABC_version=3.4.5
array[2] = instancefile3
array[2][0] = XYZ_version=1.1
(I know my notation for referencing subarrays is not correct - I'm rusty on my perl.)
How might I do that?
(I've been doing it with just bash arrays and grep and then reiterating through the initial grep output with my first array and doing another grep to fill another array - but this seems like it is going through the data more than one time, instead of building it on the fly.)
The idea is for it to build each array as it sees it. It sees "fileinstance1", it stores the values to the right in that array, as it sees it. Then if it sees "fileinstance2", it creates that array and populates with those values, all in one pass. I believe perl is the best tool for this?
Unless you can guaranteed the records with the same key will be next to each other, it's easier to start with a HoA.
my %data;
while (<>) {
chomp;
my ($key, $val) = split /:/;
push #{ $data{$key} }, $val;
}
Then convert to AoA:
my #data = values(%data);
Order-preserving:
my %data;
my #data;
while (<>) {
chomp;
my ($key, $val) = split /:/;
push #data, $data{$key} = []
if !$data{$key};
push #{ $data{$key} }, $val;
}
I’m trying to filter an array of terms using another array in Perl. I have Perl 5.18.2 on OS X, though the behavior is the same if I use 5.010. Here’s my basic setup:
#!/usr/bin/perl
#use strict;
my #terms = ('alpha','beta test','gamma','delta quadrant','epsilon',
'zeta','eta','theta chi','one iota','kappa');
my #filters = ('beta','gamma','epsilon','iota');
foreach $filter (#filters) {
for my $ind (0 .. $#terms) {
if (grep { /$filter/ } $terms[$ind]) {
splice #terms,$ind,1;
}
}
}
This works to pull out the lines that match the various search terms, but the array length doesn’t change. If I write out the resulting #terms array, I get:
[alpha]
[delta quadrant]
[zeta]
[eta]
[theta chi]
[kappa]
[]
[]
[]
[]
As you might expect from that, printing scalar(#terms) gets a result of 10.
What I want is a resulting array of length 6, without the four blank items at the end. How do I get that result? And why isn’t the array shrinking, given that the perldoc page about splice says, “The array grows or shrinks as necessary.”?
(I’m not very fluent in Perl, so if you’re thinking “Why don’t you just...?”, it’s almost certainly because I don’t know about it or didn’t understand it when I heard about it.)
You can always regenerate the array minus things you don't want. grep acts as a filter allowing you to decide which elements you want and which you don't:
#!/usr/bin/perl
use strict;
my #terms = ('alpha','beta test','gamma','delta quadrant','epsilon',
'zeta','eta','theta chi','one iota','kappa');
my #filters = ('beta','gamma','epsilon','iota');
my %filter_exclusion = map { $_ => 1 } #filters;
my #filtered = grep { !$filter_exclusion{$_} } #terms;
print join(',', #filtered) . "\n";
It's pretty easy if you have a simple structure like %filter_exclusion on hand.
Update: If you want to allow arbitrary substring matches:
my $filter_exclusion = join '|', map quotemeta, #filters;
my #filtered = grep { !/$filter_exclusion/ } #terms;
To see what's going on, print the contents of the array in each step: When you splice the array, it shrinks, but your loop iterates over 0 .. $#terms, so at the end of the loop, $ind will point behind the end of the array. When you use grep { ... } $array[ $too_large ], Perl needs to alias the non-existent element to $_ inside the grep block, so it creates an undef element in the array.
#!/usr/bin/perl
use warnings;
use strict;
use feature qw{ say };
my #terms = ('alpha', 'beta test', 'gamma', 'delta quadrant', 'epsilon',
'zeta', 'eta', 'theta chi', 'one iota', 'kappa');
my #filters = qw( beta gamma epsilon iota );
for my $filter (#filters) {
say $filter;
for my $ind (0 .. $#terms) {
if (grep { do {
no warnings 'uninitialized';
/$filter/
} } $terms[$ind]
) {
splice #terms, $ind, 1;
}
say "\t$ind\t", join ' ', map $_ || '-', #terms;
}
}
If you used $terms[$ind] =~ /$filter/ instead of grep, you'd still get uninitialized warnings, but as there's no need to alias the element, it won't be created.
I've looked through several threads on websites including this one to try and understand why I am getting an undeclared variable error for my usage of my $line . Each element of the #lines array is an array of strings.
The error is in line 25 and 27 with the $line[$count] statement
use strict;
use warnings;
my #lines;
my #sizes;
# read input from stdin file into 2d array
while(<>)
{
push(#lines, my #tokens = split(/\s+/, $_));
}
# search through each array for largest sizes in
# corresponding elements
for (my $count = 0; $count <= 5; $count++)
{
push(#sizes, 0);
foreach my $line (#lines)
{
if(length($line[$count])>$sizes[$count])
{
$sizes[$count] = length($line[$count]);
}
}
}
I can post the full code if it is necessary, but I am pretty sure the error must be in here somewhere.
The problem is here:
push(#lines, my #tokens = split(/\s+/, $_));
Pushing one array into another just adds all elements to the first array. So you are making a really long one dimensional array.
To fix this, use brackets to make an array reference:
push #lines, [ split(/\s+/, $_) ]; #No need for a temp variable.
Also, to access the array reference, you have to de-reference it. Both of these syntaxes are options:
${$line}[$count];
$line->[$count];
I think the second syntax is more readable.
Update: Also, you could simplify your code if you keep track of the longest lengths while you go through the file:
use strict;
use warnings;
use List::Util qw/max/;
my #lines;
my #sizes = (0)x6;
while(<>)
{
push #lines, [ my #tokens = split ];
#sizes = map { max ( length($tokens[$_]), $sizes[$_] ) } 0..$#tokens;
}
Note: The Data::Dumper core module is an invaluable tool when working with complex data structures in Perl.
use Data::Dumper;
print Dumper #lines;
This will print out the complete structure of whatever variable you give it. That way you can see if you actually created what you thought you did.
I'm trying to create an unique array regardless of its original order and using no module, this's what I've come up with so far:
my #arr = qw(b a a c d g e f);
my %hash;
#hash{#arr}=();
say keys %hash;
Yes. Since hash keys are unique, this is one idiomatic way to do it. The number of ways to accomplish the same thing are many.
You may also use a module, such as List::MoreUtils
use strict;
use warnings;
use List::MoreUtils qw(uniq);
print join ":", uniq qw(a a a b b c d);
Output:
a:b:c:d
Some different ways to dedupe:
my #arr = keys { map { $_ => 1 } qw(b a a c d g e f) };
The curly braces creates an anonymous hash for keys, the map statement creates a list of key/value pairs.
my #arr = dedupe(qw(a a b c d d e));
sub dedupe {
my %hash = map { $_ => 1 } #_;
return keys %hash;
}
Same thing, but in subroutine form, and split into two lines. Note that both lists will be in a semi-random order, since hashes are unordered.
The subroutine used by List::MoreUtils is equally simple, and perhaps preferable, since it will preserve the order of arguments. It still uses a hash, though.
sub uniq {
my %seen = ();
grep { not $seen{$_}++ } #_;
}
Yes you are using the correct way but there are many other ways as well to create a unique array.
see perlfaq4: How can I remove duplicate elements from a list or array? for more details.
A unique array with no ordering a.k.a. a set. I know you said 'no module' (why?!). But if you change your mind, try Set::Object or Set::Scalar