I have a big CSV file with about 30 columns and 2.5K rows.

Some of the rows have exactly the same values except some columns.

I would like to merge those alike and concatenate with a comma between the values of the columns that are not the same.

Small example:

```
id  name  age  kid
1   Tom   40   John
1   Tom   40   Roger
---merged becomes---
1   Tom   40   John, Roger

```

I can do this with PHP using lots and lots of fors and ifs but I am hoping that there's a more elegant and fast way.