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rvariable-namesmodel.matrix

R: Renaming when using model.matrix

When running the following R code:

y <- rnorm(100)  
B <- matrix(rnorm(200), ncol=2)  
colnames(B) <- c("x1", "x2")  
A <- model.matrix(y~B)  
colnames(A)

model.matrix adds to the variable names the prefix "B" in the matrix A. How can I avoid this behavior (or rename it but in a very general setting, e.g. within a function with user supplied formula)?

Solution

  • We can use sub to remove the first character in the column names.

    colnames(A)[-1] <- sub("^.", "", colnames(A)[-1])

    Or set the column names by concatenating with the ones from 'B'

    colnames(A) <- c(colnames(A)[1], colnames(B))

    Another option without using the sub would be to create a data.frame with 'y' and 'B' matrix and then use y ~.

    A <- model.matrix(y~., data=data.frame(y, B))
colnames(A)
#[1] "(Intercept)" "x1"          "x2"