CODEWITHSUNDEEP
rdplyrevaltidy
Стив Риедо
Стив Риедо

Reputation: 65

How to use tidy evaluation with column name as strings?

I've read most of the documentation about tidy evaluation and programming with dplyr but cannot get my head around this (simple) problem.

I want to programm with dplyr and give column names as strings as input to the function.

df <- tibble(
  g1 = c(1, 1, 2, 2, 2),
  g2 = c(1, 2, 1, 2, 1),
  a = sample(5),
  b = sample(5)
)

my_summarise <- function(df, group_var) {
  df %>%
    group_by(group_var) %>%
    summarise(a = mean(a))
}

my_summarise(df, 'g1')

This gives me Error : Column 'group_var' is unknown.

What must I change inside the my_summarise function in order to make this work?

Upvotes: 3

Views: 1192

Answers (3)

Kay
Kay

Reputation: 2332

You can also use sym and !!

my_summarise <- function(df, group_var) {


  df %>%
    group_by(!!sym(group_var)) %>%
    summarise(a = mean(a))
   }

my_summarise(df, 'g1')

# A tibble: 2 x 2
     g1     a
  <dbl> <dbl>
1     1  3.5 
2     2  2.67

Upvotes: 1

akrun
akrun

Reputation: 887941

We can use also ensym with !!

my_summarise <- function(df, group_var) {


  df %>%
    group_by(!!rlang::ensym(group_var)) %>%
    summarise(a = mean(a))
   }

my_summarise(df, 'g1')

Or another option is group_by_at

my_summarise <- function(df, group_var) {


      df %>%
        group_by_at(vars(group_var)) %>%
        summarise(a = mean(a))
       }

my_summarise(df, 'g1')

Upvotes: 3

Vishal Katti
Vishal Katti

Reputation: 652

Convert the string column name to a bare column name using as.name() and then use the new {{}} (read Curly-Curly) operator as below:

library(dplyr)

df <- tibble(
  g1 = c(1, 1, 2, 2, 2),
  g2 = c(1, 2, 1, 2, 1),
  a = sample(5),
  b = sample(5)
)

my_summarise <- function(df, group_var) {

  grp_var <- as.name(group_var)

  df %>%
    group_by({{grp_var}}) %>%
    summarise(a = mean(a))
}

my_summarise(df, 'g1')

Upvotes: 4

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