How do I read a file into a matrix in bash? - bash

Question

I have a text file like this
A;green;3
B;blue;2
A;red;4
C;red;2
C;blue;3
B;green;3
I have to write a script that if started with parameter "B" gives me the color of the row with the biggest number (from the rows starting with B). In this case it would be the last line, so the output would be "green".
How do I separate the elements by ";"-s and newlines and store them into a matrix so I can work with it? Do I even need to do that, or is there an easier solution?
Thanks in advance!

Answer 1

awk + sort solution:
awk -v param="B" -F';' '$1==param{ print $2; exit }' <(sort -t';' -k1,1 -k3nr file.txt)
The output:
green
Or in addition to #William Pursell's answer - to extract only color value:
awk -F';' '/^B/ && $3>m{ m=$3; c=$2 }END{ print c }' file.txt
green
Via bash script:
get_max_color.sh script:
#!/bin/bash
awk -F';' -v p="$1" '$0~"^"p && $3>m{ m=$3; c=$2 }END{ print c }' "$2"
Usage:
bash get_max_color.sh B "file.txt"
green

Answer 2

You just need to filter out the appropriate lines and store the one with the max value seen. The obvious solution is:
awk '/^B/ && $3 > m{s=$0} END { print s}' FS=\; input
To use a parameter, do
awk "/^$1/"' && $3 > m{s=$0} END { print s}' FS=\; input

Answer 3

A non-awk solution, possibly less elegant and slower than the already proposed solution:
sort -r -t\; -k1,1 -k3 file | uniq -w1 | grep "B" | cut -f2 -d\;

Answer 4

awk to the rescue!
probably not understood what you want to achieve but
awk -v key="$c" -F\; 'm[$1]<$3{m[$1]=$3; c[$1]=$2} END{print c[key]}' file
will pick the highest coded color from the file for the key
some poor usage pattern
$ for c in A B C;
do
echo $c "->" $(awk -v key="$c" -F\; 'm[$1]<$3 {m[$1]=$3; c[$1]=$2}
END {print c[key]}' file);
done;
A -> red
B -> green
C -> blue
you can probably implement the rest of the script in awk and do this process once.
Or, perhaps you want an associative array, can be done as below:
$ declare -A colors;
while IFS=\; read k c _ ;
do
colors[$k]=$c;
done < <(sort -t\; -k1,1 -k3nr file | uniq -w1)
$ echo ${colors[A]}
red