Got an error message when using summarise inside for loop

Question

Having a list containing 244 data frames. This list is called d, and d[[1]] looks like this.

d[[1]]

   year  pos  days   sal
1  2009  A     31   2000
2  2009  B     60   4000
3  2009  C     10    600
4  2010  B     10   1000
5  2010  D     90   7000

I would like to group data by year, adding days and sal, and select pos where days is maximum in the group.

The result is like:

 year   pos  days   sal
1 2009    B    101   6600
2 2010    D    100   8000

I know how to do this when it comes to the case doing it to only one data frame. I did it this way:

library(dplyr)
ygroup<-group_by(d[[1]]$year)
summarise(ygroup, pos = pos[which.max(days)], days = sum(days), sal = sum(sal))

But I want to do this same operation to the 244 data frames in the list d. I tried this:

e<-list()
ygroup<-list()
for(i in 1:244){
ygroup[[i]]<-group_by(d[[i]]$year)
e[[i]]<-summarise(ygroup[[i]], pos = pos[which.max(days)], days = sum(days), sal = sum(sal))
}

But this doesn't work, an error showing up.

Error: expecting a single value

(I think this part; pos = pos[which.max(days)] is making the problem, but I'm not that sure...) How can I solve this...?

Any comments will be greatly appreciated! :)

Try with lapply i.e. lapply(d, functiion(x) x %>% group_by(year) %>% summarise(pos = pos[which.max(days)], days = sum(days), sal = sum(sal))) — akrun
– akrun, Commented Nov 1, 2016 at 13:19

akrun · Accepted Answer · 2016-11-01 13:26:14Z

4

We can use lapply with anonymous function call to loop over the list of data.frames ('d')

lapply(d, function(x) x %>% 
                       group_by(year) %>% 
                       summarise(pos = pos[which.max(days)], 
                                 days = sum(days), sal = sum(sal)))

answered Nov 1, 2016 at 13:26

akrun

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Comments

Morgan Ball · Accepted Answer · 2016-11-01 13:24:23Z

1

Your error is in e[[i]]<- you might be better off using lapply rather than looping

ygroup<-lapply(ygroup,FUN=group_by,d$year)
e<-lapply(ygroup,FUN=summarise,pos = max(days), days = sum(days), sal = sum(sal))

Which will return a list so no need for e<-list()

answered Nov 1, 2016 at 13:24

Morgan Ball

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