Add specific value to a data.frame column by matching a pattern

Question

I have two data.frames:

pattern <- data.frame(pattern = c("A", "B", "C", "D"), val = c(1, 1, 2, 2))

match <- data.frame(match = c("A", "C"))

I want to add to my data.frame pattern another column called new_val and assign "X" to each row where the value for column pattern is in the data.frame match otherwise assign "Y"

is.element(pattern$pattern, match$match)

[1] TRUE FALSE TRUE FALSE

So, the resulting data.frame should look like:

    pattern val new_val
1   A       1   X
2   B       1   Y
3   C       2   X
4   D       2   Y

I achieved to do it with an ugly for-loop but I am sure this can be pretty much done in a one line R command using fancy stuff :-)

Is anyone able to help?

Many thanks!

Dason · Accepted Answer · 2012-07-16T15:55:51.767

I'm only really posting this since Tyler said "if you wanted a one liner data.table would likely do it" and I knew it was definitely possible with a one liner in base. I am also assuming match had been renamed to mat.

  pattern$new_val <- c("Y", "X")[(pattern$pattern %in% mat)+1]
  pattern
#  pattern val new_val
#1       A   1       X
#2       B   1       Y
#3       C   2       X
#4       D   2       Y

pattern$pattern %in% mat is finding which of the elements of pattern are in mat which returns TRUE if it's in mat, FALSE if it's not. Then I add 1 to make it numeric in the range of 1-2 so that it can be used for indexing. Then we use that as an index to the self defined vector c("Y", "X") and since the index we created is always 1 or 2 we're always able to grab an element of interest. So in this case we'll grab "Y" if pattern wasn't in mat and "X" if it was - which is what you wanted.

Indeed! Both solutions are great R code and def better than for-loop solution. Thanks very much again! — user969113, Jul 16 '12 at 15:33

Tyler Rinker · Answer 2 · 2017-07-06T13:47:30.510

Here's one way (I renamed your match to mat since there's a pretty important base function named match that you could actually use to solve this problem; in fact %in% is a form of match:

pattern <- data.frame(pattern = c("A", "B", "C", "D"), val = c(1, 1, 2, 2))
mat <- c("A", "C")

pattern$new_val <- "Y"                            #pre allot everything to be Y
pattern$new_val[pattern$pattern %in% mat] <- "X"  #replace any A or C with an X
pattern

PS if you wanted a one liner data.table would likely do it.

If you wanted something a little more complicated you could use a function from a package I'm working on:

library(qdap)

#original problem
pattern$new_val <- text2color(pattern$pattern, list(c("A", "C")), c("X", "Y"))

#extending it
#makes D  a 5
text2color(pattern$pattern, list(c("A", "C"), "D"), c("X", 5, "Y"))

This function really is designed to do something else but if you want to grab the essential parts of it you can look at the source code.

Theoretically you could update this to not require installing from github — Dason, Jul 05 '17 at 15:07

Add specific value to a data.frame column by matching a pattern

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