How quickly indexing with numeric can burn you

2014-09-18_numeric-index-gotcha.md

Inspired by recent @johnmyleswhite tweets on indexing (though they focus more on NA stuff)

My standard advice to R novices is "don't worry about numeric vs integer too much, for now", but I just created an indexing example that scares me.

I did not realize it was sooo easy to create this gotcha when indexing with numeric (which I know is not a great idea).

x <- 4:1 + 0.1
str(x <- x - 0.1)

##  num [1:4] 4 3 2 1

(1:4)[4:1]

## [1] 4 3 2 1

(1:4)[x]

## [1] 3 3 2 1

---

title: "2014-09-18_numeric-index-gotcha.r" author: "jenny" date: "Thu Sep 18 07:46:47 2014"

2014-09-18_numeric-index-gotcha.r

#' ---
#' output:
#'   html_document:
#'     keep_md: TRUE
#' ---

#' Inspired by recent @johnmyleswhite tweets on indexing (though they focus more
#' on NA stuff)  
#' 
#' My standard advice to R novices is "don't worry about numeric vs integer too
#' much, for now", but I just created an indexing example that scares me.  
#' 
#' I did not realize it was sooo easy to create this gotcha when indexing with
#' numeric (which I know is not a great idea).  

x <- 4:1 + 0.1
str(x <- x - 0.1)
(1:4)[4:1]
(1:4)[x]