Function takes an argument literally rather than the value of the argument

user_10542019 0
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I tried to create a function that would return me x largest MOLECULES based on how many unique PATIENT_ID each of them has, in descending order. That from a certain date until the last.

data <- data.frame(PATIENT_ID = c(1,1,2,2), dateM = c(ymd("2020-01-05","2020-01-06","2020-05-06","2019-12-15")), MOLECULES = c("mol1", "mol1", "mol1", "mol2"))


topx <- function(data, datefrom, var ,  x = 5){
  data %>%
  subset(dateM >= datefrom) %>%
  group_by(var) %>%
  summarize(pat = length(unique(PATIENT_ID))) %>%
  arrange(-pat) %>% 
  head(x) %>% 
  select(1)
}

topx(data = data, datefrom = "2016-04", var = MOLECULES, x = 2)

The wanted result in this case would be would be:

c("mol1","mol2")

However, it takes var as text and doesnt parse the MOLECULES in and tells me that.

 Error: Must group by variables found in `.data`.
* Column `var` is not found.
dplyr r function
2 Answers

Cool function. There are special rules and operations when programming with dplyr. See more here. Specifically, you need the {{}} operator.


library(tidyverse)
library(lubridate)
#> 
#> Attaching package: 'lubridate'
#> The following objects are masked from 'package:base':
#> 
#>     date, intersect, setdiff, union

data <- data.frame(PATIENT_ID = c(1,1,2,2), dateM = c(ymd("2020-01-05","2020-01-06","2020-05-06","2019-12-15")), MOLECULES = c("mol1", "mol1", "mol1", "mol2"))

topx <- function(data, datefrom, var ,  x = 5){
  data %>%
    subset(dateM >= datefrom) %>%
    group_by({{var}}) %>%
    summarize(pat = length(unique(PATIENT_ID))) %>%
    arrange(-pat) %>% 
    head(x) %>% 
    select(1)
}

topx(data = data, datefrom = "2016-04-01", var = MOLECULES, x = 2) 
#> `summarise()` ungrouping output (override with `.groups` argument)
#> # A tibble: 2 x 1
#>   MOLECULES
#>   <chr>    
#> 1 mol1     
#> 2 mol2

Created on 2021-01-14 by the reprex package (v0.3.0)

user_105567870

I believe this is a quasi quotation issue. !! does a one-to-one evaluation of an expression. For more information see https://adv-r.hadley.nz/quasiquotation.html

Try:

topx <- function(data, datefrom, var ,  x = 5){
  var <- enquo(var)
  data %>%
  subset(dateM >= datefrom) %>%
  group_by(!!var) %>%
  summarize(pat = length(unique(PATIENT_ID))) %>%
  arrange(-pat) %>% 
  head(x) %>% 
  select(1)
}
user_74988390
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