Indexing with names is good!!

Number of ‘high’ values:

y <- rnorm(1e4)
# cutoffs:
x <- c(1, 2, 3)
sum(y > x[3])

## [1] 15

x <- c(1, 1.5, 2.5, 3)
sum(y > x[3])

## [1] 56

Wait, let’s add another level:

x <- c(low=1, "lowish"=1.5, 'highish'=2.5, high=3)
sum(y > x['high'])

## [1] 15

BUT: A warning about factors

f <- factor(c('low', 'med', 'high'))
x <- c(low=1, med=2, high=3)

What is x[f[3]]?

x[f[3]]

## low 
##   1

Defensive programming

xf <- x[f]
stopifnot(all(names(xf) == f))

## Error in templater::render_template("Week_14_Interludes.Rmd", output = "Week_14_Interludes.md", : all(names(xf) == f) is not TRUE

xf <- x[as.character(f)]
stopifnot(all(names(xf) == f))