why does map_if() not work within a list

Question

Please help me

1) Why does map_if not work within a list
2) Is there a way to make it work
3) If not, what are the alternatives

Thanks in advance.

library(dplyr) 
library(purrr) 

cyl <- split(mtcars, mtcars$cyl) 

# This works
map_if(mtcars, is.numeric, mean) 

# This does not work 
map_if(cyl, is.numeric, mean)

Axeman · Accepted Answer · 2019-07-31T18:09:12.420

6

Because you need to map to one lever lower, the columns are at level 2. So you can do:

map(cyl, ~map_if(., is.numeric, mean))

Or:

map(cyl, map_if, is.numeric, mean)

Without the if one could do

map_depth(cyl, 2, mean)

edited Jul 31 '19 at 18:09

answered Mar 14 '17 at 10:03

Axeman

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thank you soooo much. I tried map(cyl, map_if(is.numeric, mean)), I came so close. It is super clear to me now. This will make life that much easy. Thank you once again! – cephalopod Mar 14 '17 at 10:08
One more option added. – Axeman Mar 14 '17 at 10:09
1

Update: `at_depth()` is defunct, use `map_depth()` instead – Tung Jul 31 '19 at 16:42

score 3 · Answer 2 · edited Mar 14 '17 at 10:02

3

You can try lapply:

lapply(cyl, function(x) map_if(x, is.numeric, mean))

You are attempting to use map_if() over a list of data.frames. The predicate will be tested against each data.frame, rather than each column of the data.frame e.g.

is.numeric( cyl[[1]] )
#  [1] FALSE

And that is because...

is.data.frame( cyl[[1]] )
#  [1] TRUE

edited Mar 14 '17 at 10:02

Simon O'Hanlon

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answered Mar 14 '17 at 09:50

count

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works like magic! Thanks a ton. I tried without success "map(map_if(cyl, is.numeric, mean))" – cephalopod Mar 14 '17 at 09:54
1

Thanks @count. The examples make it super clear in my mind! You guys are fab. – cephalopod Mar 14 '17 at 10:10
1

@cephalopod The credit for the example goes to @Simon O`Hanlon, I only prvided the code ;) – count Mar 14 '17 at 10:20

score 0 · Answer 3 · answered Mar 14 '21 at 18:19

0

map_if(cyl, is.numeric, mean) %>%as_tibble() This is pipable for plotting, summarizing, mutating, etc.

answered Mar 14 '21 at 18:19

ibm

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why does map_if() not work within a list

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