Same difference in alternate rows per sub group

Question

I have data frame where i need to find difference but for every alternate row the difference should stay same as the things to do are same like this:

but I have used this:

things <- data.frame( category = c("A","B","A","B","A","B","A","B","A","B"),
                      things2do = c("ball","ball","bat","bat","hockey","hockey","volley ball","volley ball","foos ball","foos ball"),
                      number = c(12,5,4,1,0,2,2,0,0,2))


    things %>% 
      mutate(diff = number - lead(number,order_by=things2do))

but it is not helpful,as I am getting this:

Can i get some help here?

[How to make a great R reproducible example?](https://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example) — zx8754, Jun 08 '17 at 21:08
Just for this sample data, you could do: `group_by(things, things2do) %>% mutate(difference = diff(number))`. — jazzurro, Jun 08 '17 at 23:09
@jazzuro that does not work, as your method gives difference between consecutive numbers. — Sana Ali, Jun 09 '17 at 03:38

www · Accepted Answer · 2017-06-08T22:00:56.780

1

library(tidyverse)

things2 <- things %>%
  spread(category, number) %>%
  mutate(diff = B - A) %>%
  gather(category, number, A:B) %>%
  select(category, things2do, number, diff) %>%
  arrange(things2do)

edited Jun 08 '17 at 22:00

answered Jun 08 '17 at 21:29

www

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HNSKD · Answer 2 · 2017-06-16T08:38:42.537

1

One way is to group the data by things2do and subsequently take an iterated difference.

library(dplyr)
things %>% 
  group_by(things2do) %>%
  mutate(diff = diff(number))

edited Jun 16 '17 at 08:38

answered Jun 09 '17 at 09:30

HNSKD

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Same difference in alternate rows per sub group

2 Answers2