#Given a basket of fruits basket = c("apple", "banana", "lemon", "orange", "orange", "pear", "cherry") basket = ifelse(basket == "apple", "banana" , basket) basket[basket == "lemon"] = "pear" #The latter is usually preferred, but sometimes the ifelse cannot be avoided

If you want to change multiple objects you would need an equal amount of ifelses. In the original post, here, R de jeu presented his function solution which removes the cumbersome writing. I recommend reading the orginal post if the idea isn't immediately clear.

The function given in the post by R de jeu is the following

decode <- function(x, search, replace, default = NULL) { # build a nested ifelse function by recursion decode.fun <- function(search, replace, default = NULL) if (length(search) == 0L) { function(x) if (is.null(default)) x else rep(default, length(x)) } else { function(x) ifelse(x == search[1L], replace[1L], decode.fun(tail(search, -1L), tail(replace, -1L), default)(x)) } return(decode.fun(search, replace, default)(x)) }

I'm not a big fan of recursive functions as they tend to be the slowest of all possible solutions. So I decided to do my own version of the decode function without recursion.

#Same input as in the decode function decode2 = function(x, search, replace, default=NULL){ #this is if we want the "default type" output if(!is.null(default)){ default.bol = !(x %in% search) x[default.bol] = default } for(i in seq(search)){ x[x == search[i]] = replace[i] } return(x) }

A standard for-looping with extra logical operations. Now it's time for some speed tests! Spoilers: my solution was around 20ish times faster, but with small vectors the time difference isn't that important.

#If it's worth doing, it's worth overdoing picnic.basket <- c("apple", "banana", "Lightsaber", "pineapple", "strawberry", "lemon","joy","orange", "genelec speakers", "cat", "pear", "cherry", "beer", "sonic screwdriver", "cat with a caption", "knife", "cheddar", "The Book of Proofs", "evil ladies", "cheese", "The R inferno", "smoked reindeer meat", "salmon", "Tardis", "Book of Death", "Pillows", "Blanket", "Woman") multi.dimensional.basket = sample(picnic.basket, 1000000, replace=TRUE) search = sample(picnic.basket, 10) replace = sample(picnic.basket[!(picnic.basket %in% search)], 10) #Making sure results match. sum(decode(multi.dimensional.basket, search, replace) == decode2(multi.dimensional.basket, search, replace)) sum(decode(multi.dimensional.basket, search, replace, "fig") == decode2(multi.dimensional.basket, search, replace, "fig")) system.time( decode(multi.dimensional.basket, search, replace) ) system.time( decode2(multi.dimensional.basket, search, replace) ) system.time( decode(multi.dimensional.basket, search, replace, "fig") ) system.time( decode2(multi.dimensional.basket, search, replace, "fig") )

## No comments:

## Post a Comment