CODEWITHSUNDEEP
r
Nick
Nick

Reputation: 145

Detecting a Changing Variable R

I have a data.frame as such. 

data.frame(color = c("G","G","G","R","R","R","R","R","R","R","G","G"),
           trial = c(1, 1, 1, 2, 2, 2, 3, 3, 3, 3, 4, 4))

I want to detect when the color switches for each 'trial'. Like this:

   color trial swtch
1      G     1     0
2      G     1     0
3      G     1     0
4      R     2     1
5      R     2     1
6      R     2     1
7      R     3     0
8      R     3     0
9      R     3     0
10     R     3     0
11     G     4     1
12     G     4     1

I know how to accomplish this with a for loop. But is there a simple way to accomplish this in R. I thought maybe the ave function would be useful.

Upvotes: 1

Views: 68

Answers (2)

thelatemail
thelatemail

Reputation: 93813

Here's something a little different:

x <- interaction(dat,drop=TRUE)
x <- factor(x, levels=unique(x))
levels(x)[] <- 0:1
dat$swtch <- x

#   color trial swtch
#1      G     1     0
#2      G     1     0
#3      G     1     0
#4      R     2     1
#5      R     2     1
#6      R     2     1
#7      R     3     0
#8      R     3     0
#9      R     3     0
#10     R     3     0
#11     G     4     1
#12     G     4     1

Upvotes: 3

akrun
akrun

Reputation: 886948

We can use ave by creating a logical index of comparing the adjacent elements of 'color', grouped by 'trial', and get the cummax.

 with(df1, ave(c(FALSE,color[-1]!= color[-nrow(df1)]), 
                 trial, FUN= cummax))
 #[1] 0 0 0 1 1 1 0 0 0 0 1 1

Upvotes: 1

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