How to count duplicate elements in a vector using R

Question

I need to write a function that receives 2 arguments in R: first a number = X second a vector = V I need that this function would return the max number of the identical straight occurrences of X for example: f(6, c(7,6,6,3,7,9,3,6,6,6,8,9) should return 3

I think this would ignore the x which I need to choose for "running" on the vector — user3581800, Apr 28 '14 at 15:44
Sorry- I skimmed the question and thought you just wanted the max length regardless of value. The answers provided include the ability to report for each value in the vector. — Carl Witthoft, Apr 28 '14 at 15:57

Paulo E. Cardoso · Accepted Answer · 2014-04-28T15:40:04.370

1

you may not need a function

dat <- c(7,6,6,3,7,9,3,6,6,6,8,9)

fmax <- function(x, vec){
  v <- rle(vec)
  max(v$lengths[v$values == x])
}
fmax(x=6, vec=dat)
[1] 3

when x in absent from dat

fmax <- function(x, vec){
  if(x %in% vec){
    v <- rle(vec)
    max(v$lengths[v$values == x])
  } else 0
}
fmax(x=20, vec=dat)
[1] 0

edited Apr 28 '14 at 15:40

answered Apr 28 '14 at 14:55

Paulo E. Cardoso

5,778
32
42

thanks!however, the issue is that I need a general function that would do so, and not specifically with the digit 6 or any specific vector. – user3581800 Apr 28 '14 at 15:14
this is a general function. change dat and x accordingly to get the desired output. Am I wrong? – Paulo E. Cardoso Apr 28 '14 at 15:18
and if the X is not part of the vector, how will force it to return "0" – user3581800 Apr 28 '14 at 15:33
This is an extension to your textual question. – Paulo E. Cardoso Apr 28 '14 at 15:35
should I re-write my question? – user3581800 Apr 28 '14 at 15:39
See if the answer is enough for your case but yes. In any case you should provide as much information as possible to enhance the change to receive better answers. – Paulo E. Cardoso Apr 28 '14 at 15:42

Julian · Answer 2 · 2014-04-28T15:25:46.637

0

r <- numeric()
j <- 0
X <- 6
for(i in 1:length(V){
j <- ifelse(v[i]==X,j+1,0)
r[i] <- j
}

max(r)

if you wanna have the maximal length for all elements in the vector:

a <- c(7,6,6,3,7,9,3,6,6,6,8,9)
b <- rle(a)
b <- data.frame(length=b$lengths, values=b$values)
aggregate(b, by=list(b$values), FUN=max)

edited Apr 28 '14 at 15:25

answered Apr 28 '14 at 14:56

Julian

189
1
6

thanks!however, the issue is that I need a general function that would do so, and not specifically with the digit 6 or any specific vector. – user3581800 Apr 28 '14 at 15:14

How to count duplicate elements in a vector using R

2 Answers2