R how to use grep in if statement

Question

In R I want to do a like in an if statement like the example below where I'm searching for any colors in the mix$color column that contain the word red and setting a new variable in the mix dataframe to the color red.

mix$newcolor <- if(grep("Red",mix$color) "red"

And here's some sample data for the dataframe mix:

AliceBlue BlueViolet DarkRed MediumVioletRed

I'm getting this error message:

Warning message: In if (grepl("deep red", mix$color) == TRUE) "red" : the condition has length > 1 and only the first element will be used

I think that grepl should be returning a TRUE or FALSE boolean value so that should be acceptable but I'm missing something (or a lot).

Thanks for your help.

You need the vectorized `ifelse` here instead of the normal if and else. You also don't need == true when using grepl. — talat, Feb 07 '15 at 17:05
Yes, that worked like a champ. I had considered using ifelse before but was stumped on the else part but I'll just reference mix$newcolor for the else. It will either be empty or have a converted value. Thanks. — Jazzmine, Feb 07 '15 at 17:14
One advantage of ifelse is that you can easily nest them. Let's say you want convert your colour vector to "pure" colours: `color = c("AliceBlue", "BlueViolet", "DarkRed", "MediumVioletRed", "DarkGreen"); ifelse(grepl("Red",color),"red",ifelse(grepl("Green",color),"green",ifelse(grepl("Blue",color),"blue","other")))` — xraynaud, Feb 07 '15 at 17:27

score 24 · Accepted Answer · answered Feb 07 '15 at 17:12

24

you can use grepl and an ifelse statement:

> color = c("AliceBlue", "BlueViolet", "DarkRed", "MediumVioletRed")
> ifelse(grepl("Red",color),"red","other")
[1] "other" "other" "red"  "red"

answered Feb 07 '15 at 17:12

xraynaud

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Thanks, essentially what docent discimus had provided but with sample code. – Jazzmine Feb 07 '15 at 17:17

Sven Hohenstein · Answer 2 · 2015-02-07T19:13:43.320

You don't need if or ifelse for this task. You can use sub:

color <- c("darkred", "indianred", "violetred", "deep red", 
           "Orange Red", "blue", "yellow")

sub(".*red.*", "red", color, ignore.case = TRUE)
# [1] "red"    "red"    "red"    "red"    "red"    "blue"   "yellow"

The sub command replaces all strings including the substring "red" with "red". Furthermore, I specified ignore.case = TRUE for upper- and lowercase matches.

R how to use grep in if statement

2 Answers2