%in% such a pain?
July 8, 2018
This post has been slightly modified from its original form on woodpeckR.
I keep forgetting how to select all elements of an object except a few, by name. I get the ! operator confused with the - operator, and I find both of them less than intuitive to use. How can I negate the %in% operator?
I have a data frame called electrofishing that contains observations from a fish sampling survey. One column, stratum, gives the aquatic habitat type of the sampling site. I’d like to exclude observations sampled in the “Tailwater Zone” or “Impounded-Offshore” aquatic habitats.
electrofishing <- data.frame(stratum = c("Tailwater Zone", "Tailwater Zone", "Impounded", "Main Channel Border", "Side Channel", "Impounded-Offshore", "Side Channel"),
idx = 1:7)
electrofishing stratum idx
1 Tailwater Zone 1
2 Tailwater Zone 2
3 Impounded 3
4 Main Channel Border 4
5 Side Channel 5
6 Impounded-Offshore 6
7 Side Channel 7My instinct would be to do this:
electrofishing <- electrofishing[electrofishing$stratum !%in%
c("Tailwater Zone", "Impounded-Offshore"),]Error: <text>:1:57: unexpected '!'
1: electrofishing <- electrofishing[electrofishing$stratum !
^But that doesn’t work. You can’t negate the %in% operator directly. Instead, you have to wrap the %in% statement in parentheses and negate the entire statement, returning the opposite of the original boolean vector:
I’m not saying this doesn’t make sense, but I can never remember it. My English-speaking brain would much rather say “rows whose stratum is not included in c(”Tailwater Zone”, “Impounded-Offshore”)” than “not rows whose stratum is included in c(”Tailwater Zone”, “Impounded-Offshore”)“.
Luckily, it’s pretty easy to negate %in% and create a %notin% operator. I credit this answer to user “catastrophic-failure” on this Stack Overflow question.
I didn’t even know that the Negate function existed. The more you know.
I know there are lots of ways to negate selections in R. dplyr has select() and filter() functions that are easier to use with -c(). Or I could just learn to throw a ! in front of my %in% statements. But %notin% seems a little more intuitive.
Now it’s straightforward to select these rows from my data frame.
https://stackoverflow.com/questions/38351820/negation-of-in-in-r
This one does a good job of explaining why !%in% doesn’t work.
@online{gahm2018,
author = {Gahm, Kaija},
title = {The \%Notin\% Operator},
date = {2018-07-08},
url = {https://kaijagahm.github.io/posts/2018-07-08-the-notin-operator},
langid = {en}
}