Sounds to me like he has a 2D array as such:
Row/Col Col 1(signal) Col 2(channel)
Row 1 3.009 1
Row 2 4.239 2
Row 3 1.100 3
In this case, the first dimension is the row dimension, and the second dimension is the column dimension. When the second dim is 0, all the rows contain signal info, when the second dim is 1, all the rows contain channel numbers.
You can split the 2D array into two 1D arrays. Row numbers between the two 1D arrays would still match signal data to channel number. So to make a 1D array of all rows in one column using the Index Array function, leave the first dim unwired (all rows), and wire the second dim (0 for signal, 1 for channel number).