Apply function to every value in an R dataframe

Question

I have a 58 column dataframe, I need to apply the transformation $log(x_{i,j}+1)$ to all values in the first 56 columns. What method could I use to go about this most efficiently? I'm assuming there is something that would allow me to do this rather than just using some for loops to run through the entire dataframe.

Answer 1

alexwhan's answer is right for log (and should probably be selected as the correct answer). However, it works so cleanly because log is vectorized. I have experienced the special pain of non-vectorized functions too frequently. When I started with R, and didn't understand the apply family well, I resorted to ugly loops very often. So, for the purposes of those who might stumble onto this question who do not have vectorized functions I provide the following proof of concept.

#Creating sample data
df <- as.data.frame(matrix(runif(56 * 56), 56, 56))
#Writing an ugly non-vectorized function
logplusone <- function(x) {log(x[1] + 1)}
#example code that achieves the desired result, despite the lack of a vectorized function
df[, 1:56] <- as.data.frame(lapply(df[, 1:56], FUN = function(x) {sapply(x, FUN = logplusone)}))
#Proof that the results are the same using both methods... 
#Note: I used all.equal rather than all so that the values are tested using machine tolerance for mathematical equivalence.  This is probably a non-issue for the current example, but might be relevant with some other testing functions.
#should evaluate to true
all.equal(log(df[, 1:56] + 1),as.data.frame(lapply(df[, 1:56], FUN = function(x) {sapply(x, FUN = logplusone)}))) 

Answer 2

您应该只能引用所需的列，然后执行操作，即：

df.log[,1:56] <- log(df[,1:56]+1)