applying list of functions columns in data frame

Question

I have 2 variables, a and b. a is potentially very large. b is always a vector of functions that can be applied to each column in the data frame a.

a <- data.frame(col1=c(1, 2, 3), col2=c(4, 5, 6))
b <- c(as.double, function(x) {1+x})

So the result that I want is that function b[1] is applied to col1, b[2] is applied to col2, and so on for all columns. I feel lapply should be used here but documentation seems to say that it can only have one function. I could use a loop I suppose but a "vectorised" way would be nice.

Answer 1

This is one way to do it:

results <- mapply(function(i,j) b[[i]](a[[j]]), i=1:length(b), j=1:length(a)) 

It gives you:

> results
     [,1] [,2]
[1,]    1    5
[2,]    2    6
[3,]    3    7