diff.awk


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#!/usr/bin/awk -f

### diff.awk
# numerical diff along columns

BEGIN {
    OFS = FS
    sign = "[+-]?"
    decimal = "[0-9]+[.]?[0-9]*"
    fraction = "[.][0-9]*"
    exponent = "([Ee]" sign "[0-9]+)?"
    number = "^" sign "(" decimal "|" fraction ")" exponent "$"
}

NR == 1 {
    ### orig data columns
    for (n=1; n<=NF; n++) {
        if ($n !~ number) {
            header[n] = $n
            dheader[n] = "d" $n
        }
        else {
            header[n] = "col" n
            dheader[n] = "dcol" n
        }
        printf(header[n])
        printf(OFS)
    }

    ### diff columns
    for (n=1; n<=NF; n++) {
        printf(dheader[n])
        printf(n < NF ? OFS : ORS)
    }
}

NF {
    if (NF > nf_max)
        nf_max = NF

    ### data columns
    for (y=1; y<=nf_max; y++) {
        if ($y == header[y] || $y == dheader[y])
            continue
        if ($y ~ number)
            printf(OFMT, $y)
        else
            printf("")
        printf(OFS)
    }

    ### diff columns
    for (y=1; y<=nf_max; y++) {
        if ($y == header[y] || $y == dheader[y])
            continue
        if ($y ~ number) {
            data[y] = $y
            (data_prev[y] ~ number) ? diff[y] = data[y] - data_prev[y] : diff[y] = ""
            data_prev[y] = data[y]
            printf(OFMT, diff[y])
        }
        else
            diff[y] = ""
        printf(y < nf_max ? OFS : ORS)
    }
}