Sorting mixed Strings in Perl
Sorting in Perl can be done with the use of a pre-defined function ‘sort’. This function uses a quicksort algorithm to sort the array passed to it.
Syntax: sort @array
Returns: a sorted array
Sorting of an array that contains strings in the mixed form i.e. alphanumeric strings can be done in various ways with the use of sort() function.
Example:
Input : Key_8, pub_12, pri_4 (array of strings) Output : pri_4 Key_8 pub_12
Sorting of such arrays is done by extracting the numbers from the strings which can be done in two ways:
- Using substr() Function: For the purpose of comparing the strings using the numbers, it is very essential to get numbers from strings. Based on the numbers we are going to sort the array of strings. substr() function is used to extract these numbers from the string. This function takes, no. of characters in the string excluding the numeric, as the parameter.
Note: All the alphanumeric strings in the array must be of the same size.
Example:usestrict;use5.010;# Defining array values with# alphanumeric stringsmy@x=qw(prin_4 Keys_8 pubg_12);# Use of sort and substr function# to sort the arraymy@y=sort{substr($a, 5) <=>substr($b, 5) }@x;# Printing the sorted arrayprintjoin" ",@y;Output:prin_4 Keys_8 pubg_12
-
Using Regular Expressions : Executing above code is a tough job if the alphanumeric string is a little bit complex, hence, for more simplicity, we can use Regular Expressions.
For Example- if the array consists “Keys_8_keys” then it’s difficult to handle such case, hence for proper filtering of the number from the string, Regular Expressions are used.
Note: This method doesn’t care if the alphanumeric strings are of different sizes.
usestrict;use5.010;# Sample string to extract# number frommy$str='Key_8_key';# Regular expression to extract the numbermy($number) =$str=~ /(\d+)/;# Printing the extracted numberprint"Number Extracted from Key_8_key is $number\n";# Defining the array with# Alphanumeric stringsmy@x=qw(pri_4 Key_8_key pubg_12);# Array before sortingprint"\nArray Before sorting\n";printjoin" ",sort@x;# Calling the sort function# with Regular Expressionmy@y=sort{ ($a=~ /(\d+)/)[0] <=> ($b=~ /(\d+)/)[0] }@x;# Printing the Array after sortingprint"\n\nArray After sorting\n";printjoin" ",@y;Output:Number Extracted from Key_8_key is 8 Array Before sorting Key_8_key pri_4 pubg_12 Array After sorting pri_4 Key_8_key pubg_12
String without a Number: If the array consists of strings in which some of the strings don’t have a number in it, then 0 can be used in place of that number. To check if there is no number in the string, following code is used:
my @y = sort { (($a =~ /(\d+)/)[0] || 0) (($b =~ /(\d+)/)[0] || 0) } @x;
#!/usr/bin/perl use strict; use 5.010; # Array with mixed type of strings my @x = qw(pri_4 Key pubg_12); # Function call with a Regular Expression my @y = sort { (($a =~ /(\d+)/)[0] || 0) <=> (($b =~ /(\d+)/)[0] || 0) } @x; # Printing the sorted array print join " ", @y; |
Key pri_4 pubg_12
Sorting using a Subroutine: For better modularization of code we can create separate function or subroutine in Perl and perform the sorting operation with the use of that subroutine. sort() function here takes the subroutine name as the parameter and calls the subroutine which holds the definition for sorting.
#!/usr/bin/perl use strict; use 5.010; # Defining an array with strings my @x = qw(Key_8 pri_4 pubg_12); # Calling sort function to sort # array using subroutine my @y = sort numbersort @x; # Printing the sorted array print join " ", @y; # Subroutine to sort the array sub numbersort { my ( $anum ) = $a =~ /(\d+)/; my ( $bnum ) = $b =~ /(\d+)/; ( $anum || 0 ) <=> ( $bnum || 0 ); } |
pri_4 Key_8 pubg_12
