CODEWITHSUNDEEP
rif-statement
LMHull
LMHull

Reputation: 77

How to create a variable based on another using if statement in R

I need in 2nd column a count of how many times observation is in 1st column. Here, 2nd column should have values 1,2,3,1,2,1,2. This code doesn't work.

x <- c(11,11,11,22,22,33,33) y <- c(1,1,1,1,1,1,1) df <- data.frame(x,y)

i <- 1    for (i in 1:(nrow(df)-1)){
if(df[i+1,1] == df[i,1]){df[i+1,2] <- 2}
 if(df[i+2,1] == df[i,1]){df[i+2,2 <- 3}
  else df[i+2,2] <- 1}

Upvotes: 1

Views: 49

Answers (3)

lmo
lmo

Reputation: 38520

You could also use sequence and rle like

 sequence(rle(x)$length)
[1] 1 2 3 1 2 1 2

So 

df$y <- sequence(rle(x)$length)

rle produces an object with the lengths of runs of repeated values as well as the values themselves. By feeding these lengths to sequence, we can produce counts from 1 to each of these values.

Upvotes: 0

Roman
Roman

Reputation: 17668

You can try base R:

unlist(by(x, x, seq_along), use.names = F)
# or 
ave(x, x, FUN = seq_along)

Upvotes: 1

A Gore
A Gore

Reputation: 1910

Here's a solution:

require(dplyr)
df %>% group_by(x) %>% mutate(z=cumsum(y)) %>% ungroup()
# A tibble: 7 × 3
# x     y     z
# <dbl> <dbl> <dbl>
#   1    11     1     1
# 2    11     1     2
# 3    11     1     3
# 4    22     1     1
# 5    22     1     2
# 6    33     1     1
# 7    33     1     2

Upvotes: 3

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