More Readable Code with Pipes in R

July 30, 2014
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(This article was first published on Econometrics by Simulation, and kindly contributed to R-bloggers)

Several blog posts have made mention of the 'magrittr' package which allows functional arguments to be passed to functions in a pipes style fashion (David Smith ).

This stylistic option has several advantages:

1. Reduced requirements of nested parenthesizes
2. Order of functional operations now read from left to right
3. Organizational style of the code may be improved

The library uses a new operator %>% which basically tells R to take the value of that which is to the left and pass it to the right as an argument. Let us see this in action with some text functions.

require('magrittr') # Let's play with some strings str1 = "A scratch? Your arm's off."str2 = "I've had worse." str1 %>% substr(3,9)   #[1]Evaluates to "scratch" str1 %>% strsplit('?',fixed=TRUE)#[[1]]#[1] "A scratch"        " Your arm's off." # Pipes can be chained as wellstr1 %>% paste(str2) %>% toupper()# [1] "A SCRATCH? YOUR ARM'S OFF. I'VE HAD WORSE." # Let's see how pipes might work with drawing random variables # I like to define a function that allows an element by element maximization vmax <- function(x, maximum=0) x %>% cbind(0) %>% apply(1, max)-5:5 %>% vmax# [1] 0 0 0 0 0 0 1 2 3 4 5 # This is identical to defining the function as:vmax <- function(x, maximum=0) apply(cbind(x,0), 1, max)vmax(-5:5) # Notice that the latter formation uses the same number of parenthsize# and be more readable. # However recently I was drawing data for a simulation in which I wanted to # draw Nitem values from the quantiles of the normal distribution, censor the# values at 0 and then randomize their order. Nitem  <- 100ctmean <- 1ctsd   <- .5 draws <- seq(0, 1, length.out = Nitem+2)[-c(1,Nitem+2)] %>%          qnorm(ctmean,ctsd) %>% vmax %>% sample(Nitem) # While this looks ugly, let's see how worse it would have been without pipesdraws <- sample(vmax(qnorm(seq(0, 1, length.out = Nitem+2)[-c(1,Nitem+2)]                  ,ctmean,ctsd)),Nitem) # Both functional sequences are ugly though I think I prefer the first which# I can easily read as seq is passed to qnorm passed to vmax passed to sample # A few things to note with the %>% operator. If you want to send the value to# an argument which is not the first or is a named value, use the '.' mydata <- seq(0, 1, length.out = Nitem+2)[-c(1,Nitem+2)] %>%           qnorm(ctmean,ctsd) %>% vmax %>% sample(Nitem) %>%          data.frame(index = 1:Nitem , theta = .) # Also not that the operator is not as slow as you might think it should be.# Thus: 1 + 8 %>% sqrt# Returns 3.828427 # Rather than(1 + 8) %>% sqrt# [1] 3
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