Thank you, Chrisant. That pointed me towards the solution.
I was using the split2array() function to parse a line of tab separated values into one_line[ ].
Then I copied each element of one_line[ ] to many_lines[ x ][ ], for x = 0 to 13301.
Then I copied all the values of many_lines[ x ][ y ] to sorting_array[ x ].
It seems clunky, but it allowed me to use split2array() to read lines and sort() to sort columns.
It has been a while since I programmed in SlickC and I forgot there was a difference between an array element with a null string and an unallocated array element. Most lines of the input file had seven values. Line #953 had only three values. Apparently, when the loop handled the fourth column, I managed to allocate most of the elements of sorting_array[ ] from 0 to 13301, with the notable exception of sorting_array[ 952 ].