user1482923 user1482923 - 20 days ago 5
R Question

Apply function to each cell of matrix in R

I'm trying to perform a function to each cell of a data table in R, creating a second one based on the result of this loop.. For example, imagine I have Matrix A

Ad1 Ad2 Ad3 Ad4
AA 6 0 10
AB 7 10 12
AC 0 0 15


and I'm trying to create Matrix B

Ad1 Ad2 Ad3 Ad4
AA 1 0 1
AB 1 0 1
AC 0 0 1


in a way that each cell assumes the value 1 if that cell has a value > 0 AND the sum of the column minus that cell is also greater than 0.

For instance, AA~Ad2 is 6 and the sum of the column is 7 (6 + 7 + 0 - 6); then AA~Ad2 in matrix B assumes value 1.

Is there a way to perform this without performing a loop? I've managed to do this with a loop but it is taking too long:

A = read.table(text="Ad1 Ad2 Ad3 Ad4
AA 6 0 10
AA 7 10 12
AA 0 0 15", header=TRUE)

B = read.table(text="Ad1 Ad2 Ad3 Ad4
AA 0 0 0
AA 0 0 0
AA 0 0 0", header=TRUE)

for (i in 1:nrow(B)) {
for (j in 2:ncol(B)) {
if ((sum(A[,j], na.rm = T) - ifelse(is.na(A[i,j]), 0, A[i,j]))> 0 &
ifelse(is.na(A[i,j]), 0, A[i,j]) > 0 )
{B[i,j] <- 1}
}
}

Answer

We can do this without a loop by creating two logical matrices -1) check whether the numeric column values are greater than 0 (A[-1] > 0), 2) check whether the difference of the column sums with the column values are also greater than 0. If both of them are TRUE (& condition), convert the logical matrix to binary (+) and assign it to the subset of the dataset (A[-1])

A[-1] <-  +(colSums(A[-1])[col(A[-1])]-A[-1]>0 & A[-1] > 0)
A
#  Ad1 Ad2 Ad3 Ad4
#1  AA   1   0   1
#2  AB   1   1   1
#3  AC   0   0   1