dplyr define a temporary variable in mutate function

Question

I am working with dplyr package of R. Let's say I have a data frame of names and ids

   df <- data.frame(dID=c(1  ,2  , 1 ),
                   name=c("a","a","b"))

and I want to resolve each id from another database and get the information I need.

   db <- data.frame(dID=c(1   ,2   ,3   ,4   ),
                  info1=c("A" ,"B" ,"C" ,"D" ),
                  info2=c("AA","BB","CC","DD"))

Currently, I am using the following code.

   df %>% rowwise() %>%
   mutate(INFO1 = (function(id){paste(db %>% filter(dID == id) %>% select(info1))})(dID),
          INFO2 = (function(id){paste(db %>% filter(dID == id) %>% select(info2))})(dID))

I was wondering is it possible to find a solution to avoid repeating this part of the code

db %>% filter(dID == id)

by storing it in a temporary variable. For example when I, change my code to

df %>% rowwise() %>%
   mutate(tmp <- db %>% filter(dID == dID),
         INFO1 = paste(tmp %>% select(info1)),
         INFO2 = paste(tmp %>% select(info2))
)

I get this error

Error in mutate_impl(.data, dots) : Column tmp <- db %>% filter(dID == dID) is of unsupported class data.frame

Is there any way to make the code tidier and faster?

Are you sure you need the function call? To me it looks like you could just do `df %>% left_join(db, by = "dID")`. — Marius, Aug 23 '18 at 03:44

score 1 · Accepted Answer · answered Aug 23 '18 at 03:49

I agree with Marius' comment. To demonstrate, the following reproduces the result from your rowwise dplyr chain

left_join(df, db) %>% mutate_at(vars(starts_with("info")), ~as.numeric(as.factor(.x)))
#  dID name info1 info2
#1   1    a     1     1
#2   2    a     2     2
#3   1    b     1     1

dplyr define a temporary variable in mutate function

1 Answers1