As a service to export from a nice discussion (Not by me) in Slack.

I need to take a large matrix and subtract the mean columnwise and inplace. Is there a fast way to do this?

By columnwise I mean taking the mean of the column and subtracting it.

Answer by @Oscar_Smith:

```
for i in axes(A,2)
@views A[:,i] .-= mean(A[:,i])
end
```

By @mcabbott

Or just

`A .-= mean(A, dims=1)`

The loop is faster for large arrays.

Note that it is equivalent to `A[:,i] .= A[:,i] .- mean(A[:,i])`

. Without `@views`

, both of the slices on the right would allocate.