Function with dplyr with two variables - r

Question

I am trying to carry out the following dplyr task, but within a function.
library("dplyr")
iris %>%
group_by(Species) %>%
summarise(N = sum(Petal.Width == 0.2, na.rm = T))
I was thinking along the lines of the following, which is not complete because I am unclear on the syntax.
getSummary <- function(varName,level) {
summary <- iris %>%
group_by(Species %>%
summarise_(N = interp(~sum(var == ilevel, na.rm = T),
var = as.name(varName))))
sums <- summary$N
}
In this case levels is the numeric 0.2. Are there any changes if the value is a character "0.2"?

Answer 1

dplyr is in the process of switching over from a lazyeval-powered NSE system to an rlang-powered one. On the new version (available now through the GitHub version, and soon through CRAN), you can use
library(dplyr)
getSummary <- function(varName, level) {
varName <- enquo(varName) # parse and quote variable name
iris %>%
group_by(Species) %>%
summarise(N = sum((!!varName) == level), # unquote with !! to use
var = rlang::quo_text(varName)) # turn quosure to string
}
getSummary(Petal.Width, 0.2)
#> # A tibble: 3 × 3
#> Species N var
#> <fctr> <int> <chr>
#> 1 setosa 29 Petal.Width
#> 2 versicolor 0 Petal.Width
#> 3 virginica 0 Petal.Width
# or make it accept strings
getSummary <- function(varName, level) {
iris %>%
group_by(Species) %>%
summarise(N = sum((!!rlang::sym(varName)) == level),
var = varName)
}
getSummary('Sepal.Length', 5.0)
#> # A tibble: 3 × 3
#> Species N var
#> <fctr> <int> <chr>
#> 1 setosa 8 Sepal.Length
#> 2 versicolor 2 Sepal.Length
#> 3 virginica 0 Sepal.Length
To use the old lazyeval syntax, it would look like
getSummary <- function(varName, level) {
iris %>%
group_by(Species) %>%
summarise_(N = lazyeval::interp(~sum(x == y), # formula to substitute into
x = lazyeval::lazy(varName), # substituted but unevaluated name
y = level), # value to substitute
var = ~lazyeval::expr_text(varName)) # convert expression to string (equivalent to `deparse(substitute(...))`)
}
getSummary(Sepal.Length, 5.0)
#> # A tibble: 3 × 3
#> Species N var
#> <fctr> <int> <chr>
#> 1 setosa 8 Sepal.Length
#> 2 versicolor 2 Sepal.Length
#> 3 virginica 0 Sepal.Length
# or make it accept strings
getSummary <- function(varName, level) {
iris %>%
group_by(Species) %>%
summarise_(N = lazyeval::interp(~sum(x == y),
x = as.name(varName),
y = level),
var = ~varName)
}
getSummary('Petal.Width', 0.2)
#> # A tibble: 3 × 3
#> Species N var
#> <fctr> <int> <chr>
#> 1 setosa 29 Petal.Width
#> 2 versicolor 0 Petal.Width
#> 3 virginica 0 Petal.Width