CODEWITHSUNDEEP
rdplyr
osbwh
osbwh

Reputation: 79

Is there a way in R to use previous row value (that's being created) in ifelse


I am trying to replicate a simple drag function in Excel into R.
Basically I want to create an ifelse that takes into account the value of each previous row in the SAME column that's being created (i.e. dynamically) Here is a reproducible example 

library(dplyr)
x <- c(1,1,1,15,1,1,1,24,1,1,1)
df <- data.frame(x)
df$y <- 1
df$y <- ifelse(df$x == 1, lag(df$y), lag(df$y)+1)

Here is the unwanted output 

x   y
1   NA
1   1
1   1
15  2
1   1
1   1
1   1
24  2
1   1
1   1
1   1

The above code changes y only when x > 1 and I want to keep that y+1 to the next rows until we find another x that is > 1.

The desired output of y should be something like this

desired y
NA
1
1
2
2
2
2
3
3
3
3

Upvotes: 1

Views: 877

Answers (2)

Ronak Shah
Ronak Shah

Reputation: 388797

You can use Reduce with accumulate = TRUE.

df$y <- Reduce(`+`, df$x > 1, accumulate = TRUE) + 1
df

#    x y
#1   1 1
#2   1 1
#3   1 1
#4  15 2
#5   1 2
#6   1 2
#7   1 2
#8  24 3
#9   1 3
#10  1 3
#11  1 3

If you want a tidyverse answer you can look into accumulate.

library(dplyr)
library(purrr)

df %>% mutate(y = accumulate(x > 1, `+`) + 1)

Upvotes: 1

Ian Campbell
Ian Campbell

Reputation: 24770

How about cumsum:

df$y <- cumsum(df$x != 1) + 1
df
    x y
1   1 1
2   1 1
3   1 1
4  15 2
5   1 2
6   1 2
7   1 2
8  24 3
9   1 3
10  1 3

For something more generalizable, you might try a for loop.

for(i in seq_along(df$x)) df$y[i] <- ifelse(df$x[i]==1,
                                            sum(df$y[i-1],0,na.rm = TRUE),
                                            sum(df$y[i-1],1,na.rm = TRUE))

Upvotes: 2

Related Questions