user1482923 - 1 year ago 65
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     0
AA     0     0     0

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}
}
}
``````

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)