Bash: how to count unique values in array and retrieve value with most duplicates

Question

I have a bash script that pushes different width:height values onto the end of an array. Some of the values are duplicates. What I need to do is loop through the array, count the number of occurrences for each unique value in the array and then retrieve the value with the most duplicates.

dimensions=( )
dimensions[${#dimensions[*]}]="450:180"
dimensions[${#dimensions[*]}]="360:240"
dimensions[${#dimensions[*]}]="360:240"
dimensions[${#dimensions[*]}]="640:480"
dimensions[${#dimensions[*]}]="360:240"
dimensions[${#dimensions[*]}]="640:480"

In the array above I would need to retrieve the value "360:240" since there were 3 duplicates. How can I count the unique values and end up with a variable containing the value with the most duplicates from the array?

mostDuplicates="360:240"

Can you use bash 4? If so, use an associative array and swap the keys and values. — kojiro
– kojiro, Commented Jan 8, 2013 at 17:48

choroba · Accepted Answer · 2013-01-08 17:50:28Z

4

Bash version 4 has associative arrays:

#! /bin/bash
dimensions=(
    450:180
    360:240
    360:240
    640:480
    360:240
    640:480)

declare -A count
max=0

for d in ${dimensions[@]} ; do
    if (( ++count[$d] > max )) ; then
        max=${count[$d]}
        winner=$d
    fi
done
echo Winner: $winner, $max times

answered Jan 8, 2013 at 17:50

choroba

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