解析和评估R中字符串表达式的列?

问题描述

作为流水线的一部分，我如何解析和评估R中的一串字符串表达式?

How can I parse and evaluate a column of string expressions in R as part of a pipeline?

在下面的示例中，我生成了所需的列，即 evaluated .但是我知道这不是正确的方法.我尝试采取整洁的方法.但是我只是很困惑.

In the example below, I produce my desired column, evaluated. But I know this isn't the right approach. I tried taking a tidyverse approach. But I'm just very confused.

library(tidyverse)
df <- tibble(name = LETTERS[1:3], 
             to_evaluate = c("1-1+1", "iter+iter", "4*iter-1"), 
             evaluated = NA)
iter = 1
for (i in 1:nrow(df)) {
  df[i,"evaluated"] <- eval(parse(text=df$to_evaluate[[i]]))
}
print(df)
# # A tibble: 3 x 3
# name  to_evaluate evaluated
# <chr> <chr>           <dbl>
# 1 A     1-1+1               1
# 2 B     iter+iter           2
# 3 C     4*iter-1            3

作为管道的一部分，我尝试了:

As part of a pipeline, I tried:

df %>% mutate(evaluated = eval(parse(text=to_evaluate)))
df %>% mutate(evaluated = !!parse_exprs(to_evaluate))
df %>% mutate(evaluated = parse_exprs(to_evaluate))
df %>% mutate(evaluated = eval(parse_expr(to_evaluate)))
df %>% mutate(evaluated = parse_exprs(to_evaluate))
df %>% mutate(evaluated = eval(parse_exprs(to_evaluate)))
df %>% mutate(evaluated = eval_tidy(parse_exprs(to_evaluate)))

这些工作都没有.

推荐答案

您可以尝试:

df %>%
 rowwise() %>%
 mutate(iter = 1,
        evaluated = eval(parse(text = to_evaluate))) %>%
 select(-iter)

  name  to_evaluate evaluated
  <chr> <chr>           <dbl>
1 A     1-1+1               1
2 B     iter+iter           2
3 C     4*iter-1            3

遵循此逻辑，其他可能性也可能起作用.使用 rlang :: parse_expr():

Following this logic, also other possibilities could work. Using rlang::parse_expr():

df %>%
 rowwise() %>%
 mutate(iter = 1,
        evaluated = eval(rlang::parse_expr(to_evaluate))) %>%
 select(-iter)

另一方面，我认为引用 @MartinMächler:

On the other hand, I think it is important to quote @Martin Mächler:

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