问题
I have a dataset and I want to generate the row position by group. For example
library(data.table)
data<-data.table(Position=c(1,2,3,4,5,6,7,8,9,10),
Category=c("M","M","M","M","F","F","F","M","M","F"))
I group by the Category and want to create column that is the row position by group. Something like below or with data.table
dataByGroup %>% group_by(Category) %>% mutate(positionInCategory = 1:nrow(Category))
Unable to work out how to achieve this?
Desired output:
| Position|Category | positionInCategory|
|--------:|:--------|------------------:|
| 1|M | 1|
| 2|M | 2|
| 3|M | 3|
| 4|M | 4|
| 5|F | 1|
| 6|F | 2|
| 7|F | 3|
| 8|M | 5|
| 9|M | 6|
| 10|F | 4|
回答1:
Try the following:
library(data.table)
library(dplyr)
data<-data.table(Position=c(1,2,3,4,5,6,7,8,9,10),
Category=c("M","M","M","M","F","F","F","M","M","F"))
cleanData <- data %>%
group_by(Category) %>%
mutate(positionInCategory = 1:n())
回答2:
Try
data[, new := rowid(Category)]
# or, if you're using 1.9.6 or older
data[, new := 1:.N, by=Category]
Position Category new
1: 1 M 1
2: 2 M 2
3: 3 M 3
4: 4 M 4
5: 5 F 1
6: 6 F 2
7: 7 F 3
8: 8 M 5
9: 9 M 6
10: 10 F 4
To use rowid, you'll currently need the unstable/devel version of the package.
来源：https://stackoverflow.com/questions/36893957/dplyr-generate-row-number-row-position-in-group-by