I have 2D arrays (#AoA) that contains references to other arrays of strings. Size of this #AoA is different each time. I would like to compare each of these arrays of strings to each other.
To compare first array of strings to each other I can use something like this:
for (my $i=0; $i < $#AoA; $i++) {
my $lcm = List::Compare->new( $aAoA[$i], $AoA[$i+1] );
my #intersection = $lcm->get_intersection;
if (#intersection) {
#some code here
}
But what the best way to compare Each array with Each other?
I would like the results like this:
Arr1 Arr2 …. ArrN
Arr1 x 1 match 3 matches 0 matches
Arr2 x N matches 3 matches
…. x 1 match
ArrN x
If you feel comfortable with List::Compare, then you could use it instead of my function intersect_count.
#!/usr/bin/perl
use strict;
use warnings;
use List::MoreUtils 'uniq';
use List::Util 'any';
my #AoA = ([1,2,3,4,], [3,4,5,6], [4,7,8,9], [11,22,33]);
my #hdrs = map "Array_$_", 1 .. #AoA;
my $fmt = "%-10s" . "%-10s" x #hdrs . "\n";
printf $fmt, ' ', #hdrs;
for (my $i=0; $i < $#AoA; $i++) {
my #matches;
for (my $j = $i+1; $j < #AoA; $j++) {
$matches[$j] = intersect_count( $AoA[$i], $AoA[$j]);
}
printf $fmt, $hdrs[$i], map $_ // ' ', #matches;
}
sub intersect_count {
my ($a1, $a2) = #_;
my $cnt;
for my $item (uniq #$a1) {
$cnt += any {$item eq $_} uniq #$a2;
}
return $cnt;
}
This prints
. Array_1 Array_2 Array_3 Array_4
Array_1 2 1 0
Array_2 1 0
Array_3 0
Related
I have the following code which reads in a 6x6 array from STDIN and saves it as an array of anonymous arrays. I am trying to print out each element with $arr[i][j], but the code below isn't working. It just prints out the first element over and over. How am I not accessing the element correctly?
#!/user/bin/perl
my $arr_i = 0;
my #arr = ();
while ($arr_i < 6){
my $arr_temp = <STDIN>;
my #arr_t = split / /, $arr_temp;
chomp #arr_t;
push #arr,\#arr_t;
$arr_i++;
}
foreach my $i (0..5){
foreach my $j (0..5){
print $arr[i][j] . "\n";
}
}
i and j are not the same as the variables you declared in the foreach lines. Change:
print $arr[i][j] . "\n";
to:
print $arr[$i][$j] . "\n";
warnings alerted me to this issue. You should add these lines to all your Perl code:
use warnings;
use strict;
To demonstrate the Perlish mantra that there's "more than one way to do it":
use 5.10.0; # so can use "say"
use strict;
use warnings qw(all);
sub get_data {
my ($cols, $rows) = #_;
my ($line, #rows);
my $i;
for ($i = 1; $i <= $rows and $line = <DATA>; $i++) {
chomp $line;
my $cells = [ split ' ', $line ];
die "Row $i had ", scalar(#$cells), " instead of $cols" if #$cells != $cols;
push #rows, $cells;
}
die "Not enough rows, got ", $i - 1, "\n" if $i != $rows + 1;
\#rows;
}
sub print_data {
my ($cols, $rows, $data) = #_;
for (my $i = 0; $i < $rows; $i++) {
for (my $j = 0; $j < $cols; $j++) {
say $data->[$i][$j];
}
}
}
my $data = get_data(6, 6);
print_data(6, 6, $data);
__DATA__
1 2 3 4 5 6
a b c d e f
6 5 4 3 2 1
f e d c b a
A B C D E F
7 8 9 10 11 12
Explanation:
if we use say, that avoids unsightly print ..., "\n"
get_data is a function that can be called and/or reused, instead of just being part of the main script
get_data knows what data-shape it expects and throws an error if it doesn't get it
[ ... ] creates an anonymous array and returns a reference to it
get_data returns an array-reference so data isn't copied
print_data is a function too
both functions use a conventional for loop instead of making lists of numbers, which in Perl 5 needs to allocate memory
There is also a two-line version of the program (with surrounding bits, and test data):
use 5.10.0; # so can use "say"
my #lines = map { [ split ' ', <DATA> ] } (1..6);
map { say join ' ', map qq{"$_"}, #$_ } #lines;
__DATA__
1 2 3 4 5 6
a b c d e f
6 5 4 3 2 1
f e d c b a
A B C D E F
7 8 9 10 11 12
Explanation:
using map is the premier way to iterate over lists of things where you don't need to know how many you've seen (otherwise, a for loop is needed)
the adding of " around the cell contents is only to prove they've been processed. Otherwise the second line could just be: map { say join ' ', #$_ } #lines;
I am fairly new to Perl.
I have a large array of numbers which is sorted first:
my #numbers = do {
open my $fh, '<', glob("hotfolder/*.out") or die $!;
local $/;
<$fh> =~ /\d+/g;
};
my #sorted_numbers = sort { $a <=> $b } #numbers;
The sorted values are now in the #sorted_numbers array.
Next it needs to find the missing values in this array:
my #missing;
my $i = 0;
for ( $sorted_numbers[ 0 ] .. $sorted_numbers[ -1 ] ) {
++$i, next if $_ == $sorted_numbers[ $i ];
push #missing, "$_\n";
}
This is where I need some help. I am not sure how to achieve the next step.
Each number in the array either starts with 2 (200000) or 3 (300000).
The missing values should only show between these ranges.
Let's say the first range finished at 240000. The other range will start somewhere over 300000.
Of course I do not want to return all the values outside these two ranges as missing.
I tried something along these lines but the syntax and logic is completely wrong:
foreach (my $step = #sorted_numbers) {
if ($step <= 299999) {
my $i = 0;
for ( $sorted_numbers[ 0 ] .. $sorted_numbers[ -1 ] ) {
++$i, next if $_ == $sorted_numbers[ $i ];
push #missing, "$_\n";
}
}
else ($step > 299999) {
my $i = 0;
for ( $sorted_numbers[ 0 ] .. $sorted_numbers[ -1 ] ) {
++$i, next if $_ == $sorted_numbers[ $i ];
push #missing2, "$_\n";
}
}
}
Let me know if something is unclear and I'll be happy to provide further information.
Just check the difference between neighbouring numbers. If it's more than 1 but small enough (see $gap_size below), report the missing numbers:
#!/usr/bin/perl
use warnings;
use strict;
use feature qw{ say };
my $gap_size = 50; # Tune this to your needs.
my #numbers = sort { $a <=> $b } map /\d+/g, <>;
for my $i (1 .. $#numbers) {
my $diff = $numbers[$i] - $numbers[$i-1];
if ($diff > 1 && $diff < $gap_size) {
say for $numbers[$i-1] + 1 .. $numbers[$i] - 1;
}
}
Is it possible to assign two variables the same data from an array in a Perl foreach loop?
I am using Perl 5, I think I came across something in Perl 6.
Something like this:
my $var1;
my $var2;
foreach $var1,$var2 (#array){...}
It's not in the Perl 5 core language, but List::Util has a pairs function which should be close enough (and a number of other pair... functions which may be more convenient, depending on what you're doing inside the loop):
#!/usr/bin/env perl
use strict;
use warnings;
use 5.010;
use List::Util 'pairs';
my #list = qw(a 1 b 2 c 3);
for my $pair (pairs #list) {
my ($first, $second) = #$pair;
say "$first => $second";
}
Output:
a => 1
b => 2
c => 3
The easiest way to use this is with a while loop that calls splice on the first two elements of the array each time,
while (my($var1, $var2) = splice(#array, 0, 2)) {
...
}
However, unlike foreach, this continually does a double-shift on the original array, so when you’re done, the array is empty. Also, the variables assigned are copies, not aliases as with foreach.
If you don’t like that, you can use a C-style for loop:
for (my $i = 0; $i < #array; $i += 2) {
my($var1, $var2) = #array[$i, $i+1];
...
}
That leaves the array in place but does not allow you to update it the way foreach does. To do that, you need to address the array directly.
my #pairlist = (
fee => 1,
fie => 2,
foe => 3,
fum => 4,
);
for (my $i = 0; $i < #pairlist; $i += 2) {
$pairlist[ $i + 0 ] x= 2;
$pairlist[ $i + 1 ] *= 2;
}
print "Array is #pairlist\n";
That prints out:
Array is feefee 2 fiefie 4 foefoe 6 fumfum 8
You can get those into aliased variables if you try hard enough, but it’s probably not worth it:
my #kvlist = (
fee => 1,
fie => 2,
foe => 3,
fum => 4,
);
for (my $i = 0; $i < #kvlist; $i += 2) {
our ($key, $value);
local(*key, $value) = \#kvlist[ $i, $i + 1 ];
$key x= 2;
$value *= 2;
}
print "Array is #kvlist\n";
Which prints out the expected changed array:
Array is feefee 2 fiefie 4 foefoe 6 fumfum 8
Note that the pairs offered by the List::Pairwise module, which were but very recently added to the core List::Util module (and so you probably cannot use it), are still not giving you aliases:
use List::Util 1.29 qw(pairs);
my #pairlist = (
fee => 1,
fie => 2,
foe => 3,
fum => 4,
);
for my $pref (pairs(#pairlist)) {
$pref->[0] x= 2;
$pref->[1] *= 2;
}
print "Array is #pairlist\n";
That prints out only:
Array is fee 1 fie 2 foe 3 fum 4
So it didn’t change the array at all. Oops. :(
Of course, if this were a real hash, you could double the values trivially:
for my $value (values %hash) { $value *= 2 }
The reasons that works is because those are aliases into the actual hash values.
You cannot change the keys, since they’re immutable. However, you can make a new hash that’s an updated copy of the old one easily enough:
my %old_hash = (
fee => 1,
fie => 2,
foe => 3,
fum => 4,
);
my %new_hash;
#new_hash{ map { $_ x 2 } keys %old_hash } =
map { $_ * 2 } values %old_hash;
print "Old hash is: ", join(" " => %old_hash), "\n";
print "New hash is: ", join(" " => %new_hash), "\n";
That outputs
Old hash is: foe 3 fee 1 fum 4 fie 2
New hash is: foefoe 6 fiefie 4 fumfum 8 feefee 2
A general algorithm for more than 2 variables:
while( #array ){
my $var1 = shift #array;
my $var2 = shift #array;
my $var3 = shift #array;
# other variables from #array
# do things with $var1, $var2, $var3, ...
}
PS: Using a working copy of the array to that it is preserved for use later:
if( my #working_copy = #array ){
while( #working_copy ){
my $var1 = shift #working_copy;
my $var2 = shift #working_copy;
my $var3 = shift #working_copy;
# other variables from #working_copy
# do things with $var1, $var2, $var3, ...
}
}
PPS: another way is to use indexing. Of course, that is a sure sign that the data structure is wrong. It should be an array of arrays (AoA) or an array of hashes (AoH). See perldoc perldsc and perldoc perllol.
my $i = 0;
while( $i < #array ){
my $var1 = $array[ $i++ ];
my $var2 = $array[ $i++ ];
my $var3 = $array[ $i++ ];
# other variables from #array
# do things with $var1, $var2, $var3, ...
}
PPPS: I've been asked to clarify why the data structure is wrong. It is a flatten set of tuples (aka records aka datasets). The tuples are recreated by counting of the number of data for each. But what is the reader constructing the set has a bug and doesn't always get the number right? If, for a missing value, it just skips adding anything? Then all the remaining tuples are shifted by one, causing the following tuples to be grouped incorrectly and therefore, invalid. That is why an AoA is better; only the tuple with the missing data would be invalid.
But an better structure would be an AoH. Each datum would access by a key. Then new or optional data can be added without breaking the code downstream.
While I'm at it, I'll add some code examples:
# example code for AoA
for my $tuple ( #aoa ){
my $var1 = $tuple->[0];
my $var2 = $tuple->[1];
my $var3 = $tuple->[2];
# etc
}
# example code for AoH
for my $tuple ( #aoh ){
my $var1 = $tuple->{keyname1};
my $var2 = $tuple->{key_name_2};
my $var3 = $tuple->{'key name with spaces'};
my $var4 = $tuple->{$key_name_in_scalar_variable};
# etc
}
Here is a module-less way to "loop" by an arbitrary value ($by) and output the resulting group of elements using an array slice:
#!perl -l
#array = "1".."6";
$by = 3; $by--;
for (my $i = 0 ; $i < #array ; $i += $by ) {
print "#array[$i..$i+$by]";
$i++ ;
}
As a one-liner to test (cut and paste to a Unix shell):
perl -E '#array = "1".."6"; $by = 3; $by--;
for (my $i = 0 ; $i < #array ; $i += $by ) {
say "#array[$i..$i+$by]"; $i++ }'
Output:
1 2 3
4 5 6
If you make $by = 2; it will print pairs of numbers. To get at specific elements of the resulting slice access it as an anonymous array: (e.g. [#array[$i..$i+$by]]->[1]).
See also:
How do I read two items at a time in a Perl foreach loop?
Perl way of iterating over 2 arrays in parallel
Some good responses there, including reference to natatime which is quite easy to use. It's easy to implement too - it is essentially a wrapper around the splice solutions mentioned in the responses here.
The following is not the nicest example, but I've been using autobox::Core and made an #array->natatime() "method" ;-) like this:
use autobox::Core ;
sub autobox::Core::ARRAY::natatime {
my ($self, $by) = #_;
my #copy = #$self ;
my #array ;
push #array, [splice (#copy, 0, $by) ] while #copy ;
if ( not defined wantarray ) {
print "#{ $_ } \n" for #array ;
}
return wantarray ? #array : \#array;
}
The #copy array is spliced destructively, but $self (which is how the #array in front of the autobox method -> arrow gets passed to the function) is still there. So I can do:
my #dozen = "1" .. "12" ; # cakes to eat
#dozen->natatime(4) ; # eat 4 at time
my $arr_ref = #dozen->natatime(4) ; # make a reference
say "Group 3: #{ $arr_ref->[2] }" ; # prints a group of elements
say scalar #dozen , " cakes left" ; # eat cake; still have it
Output:
1 2 3 4
5 6 7 8
9 10 11 12
Group 3: 9 10 11 12
12 cakes left
One other approach that also uses a CPAN module (I gave this answer elsewhere but it is worth repeating). This can also be done non-destructively, with Eric Strom's excellent List::Gen module:
perl -MList::Gen=":all" -E '#n = "1".."6"; say "#$_" for every 2 => #n'
1 2
3 4
5 6
Each group of elements you grab is returned in an anonymous array so the individual values are in: $_->[0] $_->[1] ... etc.
You mentioned Perl6, which handles multiple looping values nicely:
my #qarr = 1 .. 6;
my ($x, $y, $z) ;
for #qarr -> $x , $y , $z { say $x/$y ; say "z = " ~ $z }
Output:
0.5
z = 3
0.8
z = 6
For more on the Perl6 approach see: Looping for Fun and Profit from the 2009 Perl6 Advent Calendar, or the Blocks and Statements Synopsis for details. Perhaps Perl 5 will have a similar "loop by multliple values" construct one day - à la perl5i's foreach :-)
I am new to Perl and would like to multiply two arrays:
my #array1 = (1,2,3);
my #array2 = (2,4,6);
and print out as such:
# output ==
# 2 4 6
# 4 8 12
# 6 12 18
edit:
Got it
my #array1 = (1,2,3);
my #array2 = (2,4,6);
multiply_array(\#array1, \#array2);
sub multiply_array{
my ($a1, $a2)=#_;
for(my $i=0; $i<3; $i++){
for(my $j=0; $j<3; $j++){
my $x = #$a1[$i]*#$a2[$j];
print $x."\t";
}
print "\n";
}
}
The operation you are trying to do on the arrays is called a cartesian product.
Creating an array of arrays with the cartesian product:
my #product = map { my $a = $_; [map { $_ * $a } #array2] } #array1;
Printing it in a very verbose format:
use Data::Dumper;
Dumper(#product);
Just printing the product without storing it into an array:
for my $x (#array1) {
for my $y (#array2) {
print $x * $y . "\t";
}
print "\n";
}
You have passed references of the arrays to the function.
Hence you need to use -> to access the array elements.
Here's what you can do:
use strict;
use warnings;
my #array1 = (1,2,3);
my #array2 = (2,4,6);
multiply_array(\#array1, \#array2);
sub multiply_array{
my ($a1, $a2)=#_;
for(my $i=0; $i<3; $i++){
for(my $j=0; $j<3; $j++){
my $x = $a1->[$i]*$a2->[$j];
print $x."\t";
}
print "\n";
}
}
First sorry if I should have added this to my earlier question today, but I now have the below code and am having problems getting things to add up to 100...
use strict;
use warnings;
my #arr = map {int( rand(49) + 1) } ( 1..100 ); # build an array of 100 random numbers between 1 and 49
my #count2;
foreach my $i (1..49) {
my #count = join(',', #arr) =~ m/,$i,/g; # ???
my $count1 = scalar(#count); # I want this $count1 to be the number of times each of the numbers($i) was found within the string/array.
# push(#count2, $count1 ." times for ". $i); # pushing a "number then text and a number / scalar, string, scalar" to an array.
push(#count2, [$count1, $i]);
}
#sort #count2 and print the top 7
my #sorted = sort { $b->[0] <=> $a->[0] } #count2;
my $sum = 0;
foreach my $i (0..$#sorted) { # (0..6)
printf "%d times for %d\n", $sorted[$i][0], $sorted[$i][1];
$sum += $sorted[$i][0]; # try to add up/sum all numbers in the first coloum to make sure they == 100
}
print "Generated $sum random numbers.\n"; # doesn't add up to 100, I think it is because of the regex and because the first number doesn't have a "," in front of it
# seem to be always 96 or 97, 93...
Replace these two lines:
my #count = join(',', #arr) =~ m/,$i,/g; # ???
my $count1 = scalar(#count); # I want this $count1 to be the number of times each of the numbers($i) was found within the string/array.
with this:
my $count1 = grep { $i == $_ } #arr;
grep will return a list of elements where only the expression in {} evaluates to true. This is less error-prone and much more efficient than joining the entire array and using a a regex. Also note that scalar is not necessary since the variable $count1 is scalar, so perl will return the result of grep in scalar context.
You can also get rid of this line:
push(#count2, $count1 ." times for ". $i); # pushing a "number then text and a number / scalar, string, scalar" to an array.
since you are already printing the same information in your last foreach loop.
#!/usr/bin/perl
use strict; use warnings;
use YAML;
my #arr;
$#arr = 99;
my %counts;
for my $i (0 .. 99) {
my $n = int(rand(49) + 1);
$arr[ $i ] = $n;
++$counts{ $n };
}
my #result = map [$_, $counts{$_}],
sort {$counts{$a} <=> $counts{$b} }
keys %counts;
my $sum;
$sum += $_->[1] for #result;
print "Number of draws: $sum\n";
You can probably reuse some well-tested code from List::MoreUtils.
use List::MoreUtils qw/ indexes /;
...
foreach my $i (1..49) {
my #indexes = indexes { $_ == $i } #arr;
my $count1 = scalar( #indexes );
push( #count2, [ $count1, $i ] );
}
If you don't need the warns in the sum loop, then I'd recommend using sum from List:Util.
use List::Util qw/ sum /;
...
my $sum = sum map { $_->[0] } #sorted;
If you insist on the loop, rewrite it as:
foreach my $i ( #sorted ) {