#!/usr/bin/awk -f

# Public domain notice for all NCBI EDirect scripts is located at:
# https://www.ncbi.nlm.nih.gov/books/NBK179288/#chapter6.Public_Domain_Notice

# Author: Aaron Ucko

BEGIN {
    FS = "\t"
}
(NR <= 2) {
    for (c = 1;  c <= NF;  ++c) {
        data[NR,c] = $c
        # Subsequent rows will be populated lazily.
    }
}
(NR > 2) {
    for (c = 1;  c <= NF;  ++c) {
        if ( !(c in interesting)  &&  $c != data[2,c] ) {
            interesting[c] = 1
            # Belatedly fill in data for this column in previous rows.
            for (r = 3;  r < NR;  ++r) {
                data[r,c] = data[2,c]
            }
        }
        if (c in interesting) {
            data[NR,c] = $c
        }
    }    
}
END {
    for (r = 1;  r <= NR;  ++r) {
        l = ""
        for (c = 1;  c <= NF;  ++c) {
            if (c in interesting) {
                l = l "\t" data[r,c]
            }
        }
        print substr(l, 2) # Leave off initial tab.
    }
}