I have a data frame in R in the following format:

```
Treatment    Sample   Time_point   M1
        A         1            0   0.12
        A         2            0   0.45
        A         3            0   0.35
        A         1            1   0.76
        A         2            1   0.45
        A         3            1   0.41
        A         1            2   0.94
        A         2            2   0.55
        A         3            2   0.44

```

etc. There are 5 different treatments, 3 samples, and 10 time points. There are also about 50 columns of various measurements, with unrelated names - I only show the first of these, M1, here.

For each of these 50 measurements I would like to subtract the value that they hold at time zero, from all the subsequent time points. As an example, M1 would subsequently look like this:

```
 M1
 0
 0
 0
 0.64
 0
 0.06
 0.82
 0.10
 0.09

```

I can't figure out how to do this. I started by extracting the Time-point Zero values, making a repeating sequence of them, and then subtracting them. However, I've only been able to get this to work one column at a time, which is a bit convoluted. I wonder if there is a way to do it within a pipe, using group\_by and mutate to change the values of each column, but couldn't figure out a way to specify the values I need to subtract.