Bletchley Subscripting in R
http://hyperville.fr/wp-json/wp/v2/tags?post=288 [ gives the same data type as the data it is applied to.
[[ and $ extract the element and the data type is not necessarily the same as that of the data it is applied to.
$ does partial matching.
[ and [[ don’t.
$ does not evaluate.
[ and [[ evaluate their arguments.