 # Summarise across multiple columns, each with specific function

Hi all,

I'm writing a package and when trying to evaluate potential user's input I run into an issue I can't seem to solve with dplyr.

The user provides a data frame, of which I only know for sure that the first n columns are present (in example column x and y). There can be any other number of columns too, which I don't know beforehand. What I need to do in the code is make a summary of data based on the columns I know, but I would like to user to be able to specify summary functions for the columns that I don't know, so I don't have to discard them during the process.

REPREX - simplified version of actual problem with more columns

Overview
We only know for sure that column x and y will be present

``````  x         y a b
1 1 0.2002145 1 a
2 2 0.6852186 2 b
3 1 0.9168758 3 c
4 2 0.2843995 4 d
5 1 0.1046501 5 e
6 2 0.7010575 6 f
``````

The user then provides a list of summary functions for unknown columns

``````funList = c(a = sum, b = function(x) {paste0(x, collapse = "")})
``````

And out should come this:

``````# A tibble: 2 x 4
# Groups:   x 
x     y     a b
<int> <dbl> <int> <chr>
1     1 0.917     9 ace
2     2 0.701    12 bdf
``````

I figured out a way to to this using the following code

``````library(tidyverse)
set.seed(5)

#Data provided by user (only x and y are known for sure)
myData = data.frame(x = 1:2, y = runif(6), a = 1:6, b = letters[1:6])

#Summarise functions per column
funList = list(a = sum, b = function(x) {paste0(x, collapse = "")})

#Summarise the data using the user's functions
#----------------------------------------------

#First update all columns
for(name in names(funList)){
if(name %in% colnames(myData)){
myData = myData %>% group_by(x) %>%
mutate({{name}} := funList[[{{name}}]](!!sym(name)))
} else{
warning("No column with name '", name, "' exists")
}
}

#Get the summary value for y, then create the final table
myData %>% mutate(y = max(y)) %>% distinct()
``````

But this is cheating as I would love to use the summary function from dplyr instead, but I can only provide it with a list of functions that will be applied to all columns which will fail as not all have the same type of summary

``````myData %>% group_by(x) %>% summarise(
y = max(y),
across(.cols = contains(names(funList)), .fns = funList)
)
Error: Problem with `summarise()` input `..2`.
x invalid 'type' (character) of argument
i Input `..2` is `(function (.cols = everything(), .fns = NULL, ..., .names = NULL) ...`.
i The error occurred in group 1: x = 1.
Run `rlang::last_error()` to see where the error occurred.
``````

Any ideas??
PJ

1 Like

Hi,
I am trying to understand your problem. Seeing your ideal input and output as you provided, how do you summarise y-column. User did not provide any function for y (you say x and y are present), then how do you summarise y-column in your output. Thanks

It's trying to apply each function to each column, and this is throwing the error. If you use max it works.

``````funList <- list(a = max, b = max)
``````

Not sure if you can prevent this. You could perhaps write a custom function to figure out which of funList to apply.

I see y-column is summarised by "max" function. I am trying to solve it using cur_column

``````myData
#>   x         y a b
#> 1 1 0.2002145 1 a
#> 2 2 0.6852186 2 b
#> 3 1 0.9168758 3 c
#> 4 2 0.2843995 4 d
#> 5 1 0.1046501 5 e
#> 6 2 0.7010575 6 f
funList = c(a = sum, b = function(x) {paste0(x, collapse = "")})
funList = c(y=max, funList)

myData %>%group_by(x) %>%
summarise(across(all_of(names(funList)),  ~ funList[[cur_column()]](.x)))
#> # A tibble: 2 x 4
#>       x     y     a b
#> * <int> <dbl> <int> <chr>
#> 1     1 0.917     9 ace
#> 2     2 0.701    12 bdf
``````
2 Likes

Hi,

I'm sorry for the confusion! The y-column is known as well. I added it in later because in the real thing, I have one column I group by (in example x), then a few I know must be there (in example y), and then unknown ones (in example a, b). Updated the reprex text.

HI,

Amazing! That's exactly what I need!
I knew there must be an elegant solution Thanks again,
PJ

``````library(tidyverse)
set.seed(5)

myData = data.frame(x = 1:2, y = runif(6), a = 1:6, b = letters[1:6])

funList = c(a = sum, b = function(x) {paste0(x, collapse = "")})

myData %>%group_by(x) %>%
summarise(y = max(y),
across(all_of(names(funList)),
~ funList[[cur_column()]](.x)))
#> # A tibble: 2 x 4
#>       x     y     a b
#> * <int> <dbl> <int> <chr>
#> 1     1 0.917     9 ace
#> 2     2 0.701    12 bdf
``````

Created on 2021-03-07 by the reprex package (v1.0.0)

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