In bash how to transform multimap to a map of <

Question

I am processing output from a file in bash and need to group values by their keys.

For example, I have the

13,47099
13,54024
13,1
13,39956
13,0
17,126223
17,52782
17,4
17,62617
17,0
23,1022724
23,79958
23,80590
23,230
23,1
23,118224
23,0
23,1049
42,72470
42,80185
42,2
42,89199
42,0
54,70344
54,72824
54,1
54,62969
54,1

in a file and group all values from a particular key into a single line as in

13,47099,54024,1,39956,0
17,126223,52782,4,62617,0
23,1022724,79958,80590,230,1,118224,0,1049
42,72470,80185,2,89199,0
54,70344,72824,1,62969,1

There are about 10000 entries in my input file. How do I transform this data in shell ?

Answer 1

awk to the rescue!

assuming keys are contiguous...

$ awk -F, 'p!=$1 {if(a) print a; a=p=$1} 
                 {a=a FS $2} 
           END   {print a}' file

13,47099,54024,1,39956,0                                                                                                                  
17,126223,52782,4,62617,0                                                                                                                 
23,1022724,79958,80590,230,1,118224,0,1049                                                                                                
42,72470,80185,2,89199,0                                                                                                                  
54,70344,72824,1,62969,1