Calculate Character Frequency in Message using Perl - perl

Question

I am writing a Perl Script to find out the frequency of occurrence of characters in a message. Here is the logic I am following:
Read one char at a time from the message using getc() and store it into an array.
Run a for loop starting from index 0 to the length of this array.
This loop will read each char of the array and assign it to a temp variable.
Run another for loop nested in the above, which will run from the index of the character being tested till the length of the array.
Using a string comparison between this character and the current array indexed char, a counter is incremented if they are equal.
After completion of inner For Loop, I am printing the frequency of the char for debug purposes.
Question: I don't want the program to recompute the frequency of a character if it's already been calculated. For instance, if character "a" occurs 3 times, for the first run, it calculates the correct frequency. However, at the next occurrence of "a", since loop runs from that index till the end, the frequency is (actual freq -1). Similary for the third occurrence, frequency is (actual freq -2).
To solve this. I used another temp array to which I would push the char whose frequency is already evaluated.
And then at the next run of for loop, before entering the inner for loop, I compare the current char with the array of evaluated chars and set a flag. Based on that flag, the inner for loop runs.
This is not working for me. Still the same results.
Here's the code I have written to accomplish the above:
#!/usr/bin/perl
use strict;
use warnings;
my $input=$ARGV[0];
my ($c,$ch,$flag,$s,#arr,#temp);
open(INPUT,"<$input");
while(defined($c = getc(INPUT)))
{
push(#arr,$c);
}
close(INPUT);
my $length=$#arr+1;
for(my $i=0;$i<$length;$i++)
{
$count=0;
$flag=0;
$ch=$arr[$i];
foreach $s (#temp)
{
if($ch eq $s)
{
$flag = 1;
}
}
if($flag == 0)
{
for(my $k=$i;$k<$length;$k++)
{
if($ch eq $arr[$k])
{
$count = $count+1;
}
}
push(#temp,$ch);
print "The character \"".$ch."\" appears ".$count." number of times in the message"."\n";
}
}

Answer 1

You're making your life much harder than it needs to be. Use a hash:
my %freq;
while(defined($c = getc(INPUT)))
{
$freq{$c}++;
}
print $_, " ", $freq{$_}, "\n" for sort keys %freq;
$freq{$c}++ increments the value stored in $freq{$c}. (If it was unset or zero, it becomes one.)
The print line is equivalent to:
foreach my $key (sort keys %freq) {
print $key, " ", $freq{$key}, "\n";
}

Answer 2

If you want to do a single character count for the whole file then use any of the suggested methods posted by the others. If you want a count of all the occurances
of each character in a file then I propose:
#!/usr/bin/perl
use strict;
use warnings;
# read in the contents of the file
my $contents;
open(TMP, "<$ARGV[0]") or die ("Failed to open $ARGV[0]: $!");
{
local($/) = undef;
$contents = <TMP>;
}
close(TMP);
# split the contents around each character
my #bits = split(//, $contents);
# build the hash of each character with it's respective count
my %counts = map {
# use lc($_) to make the search case-insensitive
my $foo = $_;
# filter out newlines
$_ ne "\n" ?
($foo => scalar grep {$_ eq $foo} #bits) :
() } #bits;
# reverse sort (highest first) the hash values and print
foreach(reverse sort {$counts{$a} <=> $counts{$b}} keys %counts) {
print "$_: $counts{$_}\n";
}

Answer 3

I don´t understand the problem you are trying to solve, so I propose a more simple way to count the characters in a string:
$string = "fooooooobar";
$char = 'o';
$count = grep {$_ eq $char} split //, $string;
print $count, "\n";
This prints the number of $char occurrences in $string (7).
Hope this helps to write a more compact code

Answer 4

Faster solution :
#result = $subject =~ m/a/g; #subject is your file
print "Found : ", scalar #result, " a characters in file!\n";
Of course you can put a variable in the place of 'a' or even better execute this line for whatever characters you want to count the occurrences.

Answer 5

As a one-liner:
perl -F"" -anE '$h{$_}++ for #F; END { say "$_ : $h{$_}" for keys %h }' foo.txt