I have a data frame that consist of 1000 rows and 156 columns. I'm trying to subtract the first column to the next 38 columns, then subtract column 39 to the next 38, and so, but I can't find a way to do it. I'm only using ncdf4 and nothing else. Something like this

```
C1  C2  C3  C4  C5  C6  C7  C8
1   2   3   4   5   6   4   5
3   4   6   5   4   3   2   7

```

And I'd like it to be

```
C1  C2  C3  C4  C5  C6  C7  C8
0   1   2   3   4   5   3   4
0   1   3   2   1   0  -1   4

```

The logic would be 
First 38 columns - First column 

Columns 39:77 - Column 39

and so on.