Random selection of columns using linux command

Question

I have a flat file (.txt) with 606,347 columns and I want to extract 50,000 RANDOM columns, with exception of the first column, which is sample identification. How can I do that using Linux commands? My file looks like:

ID  SNP1    SNP2    SNP3
1   0   0   2
2   1   0   2
3   2   0   1
4   1   1   2
5   2   1   0

It is TAB delimited.

Thank you so much.

Cheers,

Paula.

Answer 1

awk to the rescue!

$ cat shuffle.awk

   function shuffle(a,n,k) {
     for(i=1;i<=k;i++) {
       j=int(rand()*(n-i))+i
       if(j in a) a[i]=a[j]
       else a[i]=j
       a[j]=i;
     }
   }

   BEGIN {srand()}
   NR==1 {shuffle(ar,NF,ncols)}
         {for(i=1;i<=ncols;i++) printf "%s", $(ar[i]) FS; print ""}

general usage

$ echo $(seq 5) | awk -f shuffle.awk -v ncols=5
3 4 1 5 2

in your special case you can print $1 and start the function loop from 2.

i.e. change

for(i=1;i<=k;i++) to a[1]=1; for(i=2;i<=k;i++)