For those coming to R from other languages, it seems very odd that R users import code from packages the way that they do. For instance, if you are used to Python, this is the general pattern of “using code from elsewhere”:

import math
import numpy as np
from random import randint

# Usage:
math.floor(3.2)
np.array(...)
randint()

Meanwhile, in R, you’re likely to see

library(dplyr)

data_frame(x = 1, y = "A") %>%
  mutate(z = TRUE)

… with the subtext being that users must simply know that the data_frame(), mutate(), and %>% functions are actually all from the dplyr package. Why is R so unusual here?

Recently I wanted to send some Shiny usage data from R to a certain metrics server. Since R includes write.socket() and friends for opening arbitrary network sockets, it seemed at the outset that this would be quite simple. However, I ran into an interesting roadblock along the way.

It turns out that R’s socket API only supports TCP connections, which you can confirm by looking at the source code – and in this case I needed to send UDP packets instead. This was a little surprising to me, since most other languages would include UDP support out of the box; it’s a core internet protocol, after all. For whatever reason, this seems not to be the case with R, and even after searching CRAN and GitHub I wasn’t able to find an existing package that provides UDP socket support.

To remedy this, I put together a simple way to write messages to UDP sockets from R.

In the past few years the APIs of the wildly popular tidyverse packages have coalesced around the pipe operator (%>%). R users familiar with this ecosystem of packages are now accustomed to writing “pipelines” where code is expressed as a series of steps composed with the pipe operator.

For example, plenty of data science code basically boils down to:

data() %>% transform() %>% summarise()

(This is even more evident if you subscribe to Wickham & Grolemund’s view that models are a “low-dimensional summary of your data”.)

There are plenty of resources on how to use pipes to re-write you R code. There are fewer on the implications of pipes on how R functions and package APIs are designed. What should package authors should keep in mind, knowing that their users are likely to use their functions in pipelines?

My own experience has led me to compile four principles for writing pipe- friendly APIs for R packages:

1. Only one argument is going to be “piped” into your functions, so you should design them to accommodate this. The first argument should be what you’d expect to be piped in; all other arguments should be parameters with meaningful default values. If you think you’ll always need more than one argument, consider wrapping them up in a lightweight S3 class.

2. Think carefully about the output of your functions, since this will be what is passed down the pipeline. Strive to always return a single type of output (a data frame, a numeric vector, etc). Never return NULL, because very few functions can take NULL as an input. (To signify empty values, use zero-row data frames or vectors with NA.)

3. Prefer “pure” functions – e.g. those that have no “side effects” that mutate global state – whenever possible. Users think about pipelines as a linear progression of steps. The transparency of pure functions make them easy to reason about in this fashion.

4. When your functions must have side effects (e.g. when printing or plotting), return the original object (instead of the conventional NULL) so that pipelines can continue.

I’ve found that being explicit about these design goals has improved the quality of my own package interfaces; perhaps they can be of use to others.

Recently I was working on an R package that had historically used both rjson and jsonlite to serialize R objects to JSON (before sending it off to an API). In this case we wanted to remove the rjson depdency, which was only used in a few places.

The most noticable hiccup I encountered while porting the code was during encoding of parameter lists generated in R, which looked something like

params <- list(key1 = "param", key2 = NULL,
               key3 = c("paired", "params"))

In this case, rjson produced exactly what our API was looking for:

cat(rjson::toJSON(params))
#> {"key1":"param","key2":null,"key3":["paired","params"]}

But by default the jsonlite package will behave very differently:

jsonlite::toJSON(params)
#> {"key1":["param"],"key2":{},"key3":["paired","params"]}

In the process of working on a recent choropeth piece for work, I discovered that it’s easy to stumble when moving spatial data out of R and onto the web. It’s a poorly-documented reality that many web-based mapping libraries (including both D3 and Leaflet) expect GeoJSON data to be in EPSG:4326, and it is by no means a given that that your spatial data will start off in this projection.

If you’re like me and do your spatial data pre-processing in R before exporting to GeoJSON, you may have to re-project your data before these libraries will handle them properly. Thankfully, this is fairly easy to do with the modern spatial packages.