How to filter each array elements according to a regex

Question

I have an array with elements like this:

@ORF= (MEZQFVECQWSXC*FVCXRCT*, MAEZCRTDRX*AZEFZC*AZERC*)

I want to split every array so that each elment starts with 'M' and ends with '*', no extra '*' in between.

so my example above should give me

@ORF = (MEZQFVECQWSXC*,MAEZCRTDRX*)

I thought about first splitting each elements like this:

    foreach (@ORF) {
        my $true= split /\*/, $_;
        push @ORF, $true
}

and then splicing the others out with and if statement, but this does not work.

I also considered using grep

@ORF= grep m/M.*\*/, @ORF;

But this does not affect the array.

I am getting increasingly confused and google is not helping... Please help me out?

Splice does not work that way, nor does grep. You splice an array using indexes and length, and you grep one list to another list. Read the manual and try again. — TLP
– TLP, Commented Nov 17, 2015 at 14:32

simbabque · Accepted Answer · 2015-11-18 08:34:27Z

3

You can indeed do that with split and a loop. You can also use map instead of a for loop.

use strict;
use warnings;
use Data::Printer;

my @ORF= ('MEZQFVECQWSXC*FVCXRCT*', 'MAEZCRTDRX*AZEFZC*AZERC*');
@ORF = map { (split /\*/, $_, 0 )[0] . '*' } @ORF;

p @ORF;

It will iterate over every element in @ORF and split on the *. The 0 as the thrid parameter tells split to only split once. Treat the return value as a list and only take the first element ([0]), put back the asterisk and you've got yourself a new list of strings that start with the M and ends with the asterisk.

[
    [0] "MEZQFVECQWSXC*",
    [1] "MAEZCRTDRX*"
]

Of course that assumes there are only strings that match this pattern without checking.

A simpler way would be to use substr and index to find the first occurance of the * and take the beginning of the string until that character. That's probably more like what you wanted to do with the splice, but misunderstood what that does.

@ORF = map { substr $_, 0 , index($_, '*') + 1 } @ORF;

edited Nov 18, 2015 at 8:34

answered Nov 17, 2015 at 14:43

simbabque

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2 Comments

Sobrique Over a year ago

Think you can reduce that split to (split /\*/ )[0]

TLP Over a year ago

If you use a look-behind assertion, you don't have to add the asterisk again.

Community · Accepted Answer · 2017-05-23 12:30:14Z

foreach (@ORF) {
    my $true= split /\*/, $_;
    push @ORF, $true
}

This was actually very close to the solution. There were just a couple of problems.

Firstly, you're assigning the return value from split to a scalar variable. And in scalar context, split returns the number of items it can split the string into, not the items themselves. So you'll just get the value 2. We can fix that by making it a list assignment.

my ($true) = split /\*/, $_;

Secondly, you're pushing your new value on to the end of @ORF. This means that @ORF just keeps getting longer and your loop never ends. You need to replace the current element of the array with your new value. And you can do that by assigning to $_.

So the whole loop becomes:

foreach (@ORF) {
    my ($true) = split /\*/, $_;
    $_ = "$true*";
}

Having said all that, I do prefer simbabque's map solution.

zdk · Accepted Answer · 2015-11-17 15:02:47Z

0

if you like, you could also use map+grep, like so:

use Data::Dumper;

my @ORF= ("MEZQFVECQWSXC*FVCXRCT*", "MAEZCRTDRX*AZEFZC*AZERC*");
@ORF = grep { $_ =~ /^M/ } map { (split/\*/, $_)[0] . '*' } @ORF;
print Data::Dumper->Dump(\@ORF);

Result:

$VAR1 = 'MEZQFVECQWSXC*';
$VAR2 = 'MAEZCRTDRX*';

answered Nov 17, 2015 at 15:02

zdk

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