wrapr: for sweet R code

This article is on writing sweet R code using the wrapr package.

The problem

Consider the following R puzzle. You are given: a data.frame, the name of a column that you wish to find missing values (NA) in, and the name of a column to land the result. For instance:

d <- data.frame(x = c(1, NA))print(d) #    x # 1  1 # 2 NAcname <- 'x'print(cname) # [1] "x"rname <- paste(cname, 'isNA', sep = '_')print(rname) # [1] "x_isNA"

How do you write generic code to populate the column x_isNA with which rows of x are missing?

The “base R” solution

In “base R” (R without additional packages) this is easy.

When you know the column names while writing the code:

d2 <- dd2$x_isNA <- is.na(d2$x)print(d2) #    x x_isNA # 1  1  FALSE # 2 NA   TRUE

And when you don’t know the column names while writing the code (but know they will arrive in variables later):

d2 <- dd2[[rname]] <- is.na(d2[[cname]])

The “base R” solution really is quite elegant.

The “all in” non-standard evaluation dplyr::mutate solution

As far as I can tell the “all in” non-standard evaluation dplyr::mutate solution is something like the following.

When you know the column names while writing the code:

library("dplyr")d %>% mutate(x_isNA = is.na(x))

And when you don’t know the column names while writing the code (but know they will arrive in variables later):

d %>%  mutate_(.dots =            stats::setNames(list(lazyeval::interp(              ~ is.na(VAR),              VAR = as.name(cname)            )),            rname))

The sweet wrapr::let dplyr::mutate solution

We will only work the harder “when you don’t yet know the column name” (or parametric) version:

library("wrapr")let(list(COL = cname, RES = rname),    d %>% mutate(RES = is.na(COL)))

I think that this is pretty sweet, and can really level up your dplyr game.

wrapr::let is available from CRAN and already has a number of satisfied users:

If function behavior depends on variable names, then convenient control of functions is eventually going to require convenient control of variable names; so needing to re-map variable names at some point is inevitable.