Determining next row in R

user_2845095 0
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Suppose I have this dataframe, df:

 UserID <- c(1, 1, 1, 5, 5)
 PathID <- c(1,2,3,1,2)
 Page <- c("home", "about", "services", "home", "pricing")
 df <- data.frame(UserID, PathID, Page)

   UserID PathID  Page
1  1      1       home
2  1      2       about
3  1      3       services
4  5      1       home
5  5      2       pricing

I would like to know the next Page if Page = home. Not sure how to proceed. Any direction is much appreciated.

r
3 Answers

With which and +1, you can extract the value after page == "Home".

df$Page[which(df$Page == "home") + 1]
[1] "about"   "pricing"

You can also use dplyr::lead:

dplyr::lead(df$Page)[df$Page == "home"]
[1] "about"   "pricing"
user_134606020

Another possible solution:

library(dplyr)

df %>% 
  mutate(pnext = if_else(Page == "home", lead(Page), NA_character_))

#>   UserID PathID     Page   pnext
#> 1      1      1     home   about
#> 2      1      2    about    <NA>
#> 3      1      3 services    <NA>
#> 4      5      1     home pricing
#> 5      5      2  pricing    <NA>

In case we only need the result as a vector:

library(dplyr)

df %>% 
  mutate(pnext = if_else(Page == "home", lead(Page), NA_character_)) %>% 
  filter(!is.na(pnext)) %>% 
  pull
 
#> [1] "about"   "pricing"
user_115644870

In base it could be don with:

df$Page[c(FALSE, (df$Page == "home")[-nrow(df)])]
#[1] "about"   "pricing"
user_104885040
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