How to add a cumulative column to an R dataframe using dplyr?

Question

I have the same question as this post, but I want to use dplyr:

With an R dataframe, eg:

df <- data.frame(id = rep(1:3, each = 5)                  , hour = rep(1:5, 3)                  , value = sample(1:15)) 

how do I add a cumulative sum column that matches the id?

Without dplyr the accepted solution of the previous post is:

df$csum <- ave(df$value, df$id, FUN=cumsum) 

Answer 1

Like this?

df <- data.frame(id = rep(1:3, each = 5),                  hour = rep(1:5, 3),                  value = sample(1:15))  mutate(group_by(df,id), csum=cumsum(value)) 

Or if you use the dplyr's piping operator:

df %>% group_by(id) %>% mutate(csum = cumsum(value)) 

Result in both cases:

Source: local data frame [15 x 4] Groups: id     id hour value csum 1   1    1     4      4 2   1    2    14     18 3   1    3     8     26 4   1    4     2     28 5   1    5     3     31 6   2    1    10     10 7   2    2     7     17 8   2    3     5     22 9   2    4    12     34 10  2    5     9     43 11  3    1     6      6 12  3    2    15     21 13  3    3     1     22 14  3    4    13     35 15  3    5    11     46