transform columns to binary encoded columns in R

Question

I have some nominal variables encoded as integers (not ordinal), which I would like to encode as binary (not dummies nor one hot!). The following code is what I came up with (adapted from other code I found). Is this a valid/scalable approach? Thanks!

library(binaryLogic)
df <- data.frame(x1 = c(1, 1, 2, 3), x2 = c(1, 2, 3, 4))
encode_binary <- function(x, name = "binary_") {
 x2 <- as.binary(x)
 maxlen <- max(sapply(x2, length))
 x2 <- lapply(x2, function(y) {
 l <- length(y)
 if (l < maxlen) {
 y <- c(rep(0, (maxlen - l)), y)
 }
 y
 })
 d <- as.data.frame(t(as.data.frame(x2)))
 rownames(d) <- NULL
 colnames(d) <- paste0(name, 1:maxlen)
 d
}
df <- cbind(df, encode_binary(df[["x1"]], name = "binary_x1_"))
df <- cbind(df, encode_binary(df[["x2"]], name = "binary_x2_"))
df

Answer 1

If we test on larger vector your approach is quite slow:

test_vec <- 1:1e5
system.time(v1 <- encode_binary(test_vec, name = "binary_x1_"))
# user system elapsed 
# 22.23 0.08 22.37 

Based on this SO question I managed to write code that performs a lot faster:

encode_binary2 <- function(x, name = "binary_") {
 m <- sapply(x, function(x) rev(as.integer(intToBits(x))))
 tm <- t(m)
 # remove empty bit cols
 i <- which(colSums(tm) != 0L)[1]
 tm <- tm[, i:ncol(tm)]
 # save to data.frame
 d <- as.data.frame(tm)
 rownames(d) <- NULL
 colnames(d) <- paste0(name, 1:ncol(d))
 d
}
system.time(v2 <- encode_binary2(test_vec, name = "binary_x1_"))
# user system elapsed 
# 0.61 0.02 0.63 
# test that results are equal:
all.equal(v1, v2)
# [1] TRUE