Add index column to CSV file

Question

I have a large Comma-Separated File (6GB) and would like to add an index column to it. I'm looking at Unix type solutions for efficiency. I'm using a Mac.

I have this:

V1  V2  V3
0.4625  0.9179  0.8384
0.9324  0.2486  0.1114 
0.6691  0.7813  0.6705
0.1935  0.3303  0.4336

Would like to get this:

ID  V1  V2  V3
1   0.4625  0.9179  0.8384
2   0.9324  0.2486  0.1114
3   0.6691  0.7813  0.6705
4   0.1935  0.3303  0.4336

Answer 1

This will probably work:

awk -F'\t' -v OFS='\t' '
  NR == 1 {print "ID", $0; next}
  {print (NR-1), $0}
' input.csv > output.csv

In awk, the NR variable is "the total number of input records seen so far", which in general means "the current line number". So the NR == 1 in the first line is how we match the first record and add the "ID" column header, and for the remaining lines we use NR-1 as the index.

The -F'\t' argument sets the input field separator, and -vOFS='\t' sets the output field separator.

Answer 2

Since no technology is specified in the original post, I'd be happy here to keep it simple.

(all the fancy Vim/bash solutions are fine if you know what you're doing).

• Open the CSV file in your favourite spreadsheet programme (I'm using LibreOffice, but Excel or a native Mac equivalent will do)
• insert a column to the left of column A
• Enter a 1 into cell A2, the first cell under the headers
• Double-click the blob at the bottom right of the cell as shown in the screenshot:

This last step will fill the index column with 1,2,3... etc. You can then save the resulting spreadsheet as a CSV file again.