问题描述
我正在尝试将用户输入解析为函数调用的参数(在表达式内)。看来我接近了,但是!!!用括号括住我的论点,这是行不通的。我正在尝试通过用户输入来重新创建以下内容:
+---+-------------------+-----+
| id| date|value|
+---+-------------------+-----+
| A1|2016-09-30 23:00:00| 3|
| A1|2016-10-01 00:00:00| 3|
| A1|2016-10-01 01:00:00| 1|
| A1|2016-10-01 02:30:30| 3|
| A9|2016-10-05 23:00:00| 3|
| A9|2016-10-06 00:00:00| 3|
| A9|2016-10-06 02:20:00| 4|
| A9|2016-10-06 03:20:00| Null|
+---+-------------------+-----+
recipe(mpg ~ cyl + hp + wt + disp,data = mtcars) %>%
step_log(disp,base = 10,offset = 0) %>%
prep()
我的表情最终看起来像这样:
library(rlang)
library(tidymodels)
user_dv <- "mpg"
user_idv <- c("cyl","hp","wt","disp")
user_step <- "log"
user_selector <- "disp"
user_args <- "base = 10,offset = 0"
formula <- as.formula(paste(user_dv,paste(user_idv,collapse = " + "),sep = " ~ "))
rcp <- expr(recipe(!!formula,data = mtcars))
add_step <- function(x,step,selector,args){
f <- parse_expr(paste0("step_",step))
vars <- ensym(user_selector)
args <- args %>%
str_replace(",",";") %>%
parse_exprs()
step_expr <- call2(f,vars,!!!args)
expr(!!x %>% !!step_expr)
}
rcp %>%
add_step(user_step,user_selector,user_args) %>%
eval() %>%
prep()
不准备()
解决方法
在parse_exprs()
之后,您得到的赋值表达式存储在未命名列表中:
# [[1]]
# base = 10
#
# [[2]]
# offset = 0
同时,要获得!!!
所需的效果,它们必须是命名列表中的值:
# $base
# [1] 10
#
# $offset
# [1] 0
话虽如此,我建议改为“转发点”,因为它可以导致更简单,更灵活的实现:
add_step <- function(x,step,selector,...){
f <- parse_expr(paste0("step_",step))
vars <- sym(selector)
step_expr <- call2(f,vars,...) # <---- forwarding the dots here
expr(!!x %>% !!step_expr)
}
用户现在可以直接向add_step()
直接提供所需的参数:
rcp %>% add_step(user_step,user_selector,base=10,offset=0)
# recipe(mpg ~ cyl + hp + wt + disp,data = mtcars) %>%
# step_log(disp,base = 10,offset = 0)
或将它们存储在列表中,并在您的函数上使用!!!
:
user_args <- list(base = 10,offset=0)
rcp %>% add_step(user_step,!!!user_args)