Relatively new to tidy evaluation and while the functions I'm making work, I want to know why different helper functions are used. For example, what is the difference between enquo and ensym? In the function I made below to capture daily average and moving average they're interchangeable:
library(dplyr)
library(lubridate)
library(rlang)
library(zoo)
manipulate_for_ma <- function(data, group_var, da_col_name, summary_var, ma_col_name) {
group_var <- ensym(group_var)
summary_var <- enquo(summary_var)
da_col_name <- ensym(da_col_name)
ma_col_name <- enquo(ma_col_name)
data %>%
group_by(!!group_var) %>%
summarise(!!da_col_name := mean(!!summary_var, na.rm = TRUE)) %>%
mutate(!!ma_col_name := rollapply(!!da_col_name,
30,
mean,
na.rm = TRUE,
partial = TRUE,
fill = NA)) %>%
rename(date = !!group_var)
}
lakers %>%
mutate(date = ymd(date)) %>%
manipulate_for_ma(group_var = date,
da_col_name = points_per_play_da,
summary_var = points,
points_per_play_ma)
# A tibble: 78 x 3
date points_per_play_da points_per_play_ma
<date> <dbl> <dbl>
1 2008-10-28 0.413 0.458
2 2008-10-29 0.431 0.459
3 2008-11-01 0.408 0.456
4 2008-11-05 0.386 0.457
I've read about enquo here and ensym here. Is the difference that ensym is more restrictive and only takes strings or string-like objects?
Another take :
library(rlang)
library(dplyr, warn.conflicts = FALSE)
test <- function(x){
Species <- "bar"
cat("--- enquo builds a quosure from any expression\n")
print(enquo(x))
cat("--- ensym captures a symbol or a literal string as a symbol\n")
print(ensym(x))
cat("--- evaltidy will evaluate the quosure in its environment\n")
print(eval_tidy(enquo(x)))
cat("--- evaltidy will evaluate a symbol locally\n")
print(eval_tidy(ensym(x)))
cat("--- but both work fine where the environment doesn't matter\n")
identical(select(iris,!!ensym(x)), select(iris,!!enquo(x)))
}
Species = "foo"
test(Species)
#> --- enquo builds a quosure from any expression
#> <quosure>
#> expr: ^Species
#> env: global
#> --- ensym captures a symbol or a literal string as a symbol
#> Species
#> --- evaltidy will evaluate the quosure in its environment
#> [1] "foo"
#> --- evaltidy will evaluate a symbol locally
#> [1] "bar"
#> --- but both work fine where the environment doesn't matter
#> [1] TRUE
test("Species")
#> --- enquo builds a quosure from any expression
#> <quosure>
#> expr: ^"Species"
#> env: empty
#> --- ensym captures a symbol or a literal string as a symbol
#> Species
#> --- evaltidy will evaluate the quosure in its environment
#> [1] "Species"
#> --- evaltidy will evaluate a symbol locally
#> [1] "bar"
#> --- but both work fine where the environment doesn't matter
#> [1] TRUE
test(paste0("Spec","ies"))
#> --- enquo builds a quosure from any expression
#> <quosure>
#> expr: ^paste0("Spec", "ies")
#> env: global
#> --- ensym captures a symbol or a literal string as a symbol
#> Only strings can be converted to symbols
Created on 2019-09-23 by the reprex package (v0.3.0)