Demean R data frame

Question

I would like to demean multiple columns in an R `data.frame`. Using an example from this question ``` set.seed(999) library(plyr) library(plm) # random data.frame dat <- expand.grid(id=factor(1:3), cluster=factor(1:6)) dat <- cbind(dat, x=runif(18), y=runif(18, 2, 5)) #demean x and y dat.2 <- ddply(dat, .(cluster), transform, x=x-mean(x), y=y-mean(y)) ``` My problem is that I have (lots) more than 2 variables, and I would like to avoid hard-coding this analysis. I'm new to `plyr` in general; why does this ``` dat.2 <- ddply(dat[,c(x,y)], .(cluster), transform, function(x) x - mean(x)) ``` not work? Is there some crucial step that I'm missing? Is there a better way to do this in general?

Accepted Answer

Have a look at the `colwise` functor. The only thing to be careful about is that `id` column. Hence:

```
demean <- colwise(function(x) if(is.numeric(x)) x - mean(x) else x)
dat.2 <- ddply(dat, .(cluster), demean)
```

Edit: as you found, there is even a `numcolwise` functor for only dealing with numerics so you can do:

```
demean <- numcolwise(function(x) x - mean(x))
dat.2 <- ddply(dat, .(cluster), demean)
```

You can also use the `scale` function rather than define your own function:

```
dat.2 <- ddply(dat, .(cluster), numcolwise(scale, scale = FALSE))
```

Demean R data frame

Solution

Problem