问题
I would like to have a new column with Ntile but it should depend on column 1 - "year" and show the ntile number for column 2 - "mileage".
year mileage
<dbl> <dbl>
1 2011 7413
2 2011 10926
3 2011 7351
4 2011 11613
5 2012 8367
6 2010 25125
mydata$Ntile <- ntile(mydata$mileage, 10)
I know the easy to use function ntile, but I do not know how to make it depend on 2 columns. I would like to have ntiles for mileage but for each year, 2010, 2011 and 2012 to be calculated in new column "Ntile".
PS: I know there is not enough data to calculate Ntiles for 2011 and 2012, it is just an example.
回答1:
I like the data.table approach:
library(data.table)
mydata <- as.data.table(mydata)
mydata[, Ntile:=ntile(mileage,10), by=year]
Best!
来源：https://stackoverflow.com/questions/54400557/ntile-and-decile-function-depended-on-two-columns-in-r