Calculate Percentage for each time series observations per Group in R

Question

New to R, so just my getting head around the data wrangling aspect. Tried looking for a similar question but couldn\'t find it.

I would like to add an additional c

Answer 1

library(dplyr)
df %>% group_by(date) %>% mutate( percentage = views/sum(views))
Source: local data frame [9 x 4]
Groups: date

  views       date article percentage
1  1578 2015-01-01       A  0.5698808
2   616 2015-01-01       B  0.2224630
3   575 2015-01-01       C  0.2076562
4  1744 2015-01-02       A  0.5921902
5   541 2015-01-02       B  0.1837012
6   660 2015-01-02       C  0.2241087
7  2906 2015-01-03       A  0.6955481
8   629 2015-01-03       B  0.1505505
9   643 2015-01-03       C  0.1539014

Or, if multiple identical articles are possible per day:

df %>% group_by(date) %>% mutate(sum = sum(views)) %>% 
group_by(date, article) %>% mutate(percentage = views/sum) %>% 
select(-sum)