Pfthb

Is there a way in R to replace values in each row of a matrix/dataframe with a specific value from that row?

For example, I have the following matrix:

df<-cbind(c("A","C","G","T"),c("T","G","C","A"),c(0,1,0,1),c(1,0,1,0),c(0,1,0,1))

df
# [,1] [,2] [,3] [,4] [,5]
#[1,] "A" "T" "0" "1" "0"
#[2,] "C" "G" "1" "0" "1"
#[3,] "G" "C" "0" "1" "0"
#[4,] "T" "A" "1" "0" "1"

and I want to replace the zeros in each row with the corresponding letter from the first column of that row, such that the new matrix will look like this:

newdf
# [,1] [,2] [,3] [,4] [,5]
#[1,] "A" "T" "A" "1" "A"
#[2,] "C" "G" "1" "C" "1"
#[3,] "G" "C" "G" "1" "G"
#[4,] "T" "A" "1" "T" "1"

The closest I have been able to get is with the following commands, but it does not replace the zeros with the correct values from column 1.

df[df==0]<-NA
df[, 3:ncol(df)][is.na(df[, 3:ncol(df)])] <- df[,1]

We can replicate the first column to make the lengths equal and then do the assignment based on the logical matrix. It will subset the elements that are of the same length as in the rhs

i1 <- df == 0
newdf <- df
newdf[i1] <- df[,1][row(df)][i1]
newdf
 [,1] [,2] [,3] [,4] [,5]
#[1,] "A" "T" "A" "1" "A" 
#[2,] "C" "G" "1" "C" "1" 
#[3,] "G" "C" "G" "1" "G" 
#[4,] "T" "A" "1" "T" "1"