Question

I have a file like:

file.dat

1 2
1 3
2 1
2 4
2 3
3 4

The left column is sorted. I would like to write a new file liek this:

1 2 3
2 1 4 3
3 4

In the first column should be the left column number of file.dat and next to it the right column numbers. Any help?

Answer 1

#!/bin/bash
awk -f <(cat - <<-'EOF'
  {
    b[$1, a[$1]++] = $2;
  }
  END {
    for (i in a) {
      printf "%d ", i;
      for (j = 0; j < a[i]; j++) {
        printf "%d ", b[i, j];
      }
      print ""
    }
  }
EOF
) < /dev/stdin

Output:

$ ./script.sh < file.dat 
1 2 3 
2 1 4 3 
3 4 

This script will run with awk. Name if file.awk:

{
    b[$1, a[$1]++] = $2;
}
END {
    for (i in a) {
        printf "%d ", i;
        for (j = 0; j < a[i]; j++) {
            printf "%d ", b[i, j];
        }
        print ""
    }
}

Run like this:

 awk -f file.awk < file.dat