AWK Text Processing – Sum Values in 5th Column by 2nd Column Field

processes[$0] += $1; use the whole line as key in your associative array, which is not unique. You must use $1, which is command name as key.

Try:

$ ps -A --sort -rss -o comm,pmem | awk '
  NR == 1 { print; next }
  { a[$1] += $2 }
  END {
    for (i in a) {
      printf "%-15s\t%s\n", i, a[i];
    }
  }
'

If you want to sort the output by the second field, try:

$ ps -A --sort -rss -o comm,pmem | awk '
  NR == 1 { print; next }
  { a[$1] += $2 }
  END {
    for (i in a) {
      printf "%-15s\t%s\n", i, a[i] | "sort -rnk2";
    }
  }
'

Not 100% the same output as you asked, but hopefully close enough:

function percent(value, total) {
    return sprintf("%.2f", 100 * value / total);
}
{
    label[NR] = $1
    for (i = 2; i <= NF; ++i) {
        sum[i] += col[i][NR] = $i
    }
}
END {
    title = label[1]
    for (i = 2; i <= length(col) + 1; ++i) {
        title = title "\t" col[i][1];
    }
    print title
    for (j = 2; j <= NR; ++j) {
        line = label[j]
        for (i = 2; i <= length(col) + 1; ++i) {
            line = line "\t" percent(col[i][j], sum[i]);
        }
        print line
    }
}

Produces output:

ID    Sample1 Sample2 Sample3
One   62.50   0.00    25.00
Two   18.75   60.00   40.00
Three 18.75   40.00   35.00

Run it with gawk -f script.awk file.txt

Of course, you could flatten the script to a single line, but I think it's better to keep it in a script file like this so it's easier to read and maintain.

A simpler and better version that works with BSD AWK too, not only GNU AWK:

function percent(value, total) {
    return sprintf("%.2f", 100 * value / total)
}
BEGIN { OFS = "\t" }
NR == 1 { gsub(/ +/, OFS); print; next }
{
    label[NR] = $1
    for (i = 2; i <= NF; ++i) {
        sum[i] += col[i, NR] = $i
    }
}
END {
    for (j = 2; j <= NR; ++j) {
        $1 = label[j]
        for (i = 2; i <= NF; ++i) {
            $i = percent(col[i, j], sum[i])
        }
        print
    }
}