如何在输入非数值时终止R代码执行？函数报错求助

原本运行正常的ci_boot函数，在加入非数值输入时终止代码的判断逻辑后，调用时出现错误提示：Error in ci_boot(dat = x, by = wk, var = pd) : object 'pd' not found。相关代码如下：

#DATA
library(tidyverse)
x <-  structure(list(wk = c(1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 
2, 3, 3, 3, 3, 3, 3), month = c(1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 
1, 1, 1, 1, 1, 1, 1, 1, 1, 1), xd = c(0.0370098838217444, 0.0391215970961887, 
0.0409865246890313, NA, NA, NA, NA, 0.015188, 0.007513, 0.012716, 
0.013962, 0.014259, 0.023553, 0.032122, 0.03953, 0.028946, 0.030769, 
0.030815, 0.029187, 0.022604), td = c(0.02701157274146, 0.0284158620689655, 
0.0296560389182058, NA, NA, NA, NA, 0.0125, 0.007396, 0.010856, 
0.011685, 0.011882, 0.018063, 0.023761, 0.028687, 0.021649, 0.022861, 
0.022892, 0.021809, 0.017432), pd = c(317.308439683869, 0, 126.719553152898, 
NA, NA, NA, NA, 2671.6, 3540.6976744186, 1270.35740604274, 1067.69362430466, 
688.099646524154, 317.444499806234, 420.941879550524, 280.475476696762, 
250.681324772507, 159.048160622895, 258.125109208457, 450.868907331836, 
0), year = c(2007, 2007, 2007, 2007, 2007, 2007, 2007, 2007, 
2007, 2007, 2007, 2007, 2007, 2007, 2007, 2007, 2007, 2007, 2007, 
2007)), class = "data.frame", row.names = c(NA, -20L))

x$test <- rep("hi",nrow(x))   # 测试文本输入的情况

# 原正常运行的函数
ci_boot <- function(dat, by, var, conf.int = 0.90,...) {
  dat %>%
    group_by({{by}}) %>%   
    dplyr::summarise(mean=list(smean.cl.boot({{var}}, conf.int=conf.int))) %>%
    unnest_wider(mean)
}
ci_boot(dat = x, by = wk, var = pd)

# 添加检查后报错的函数
ci_boot <- function(dat, by, var, conf.int = 0.90,...) {
  if(!is.numeric(var)) {stop("'var' must be numeric")}  # 尝试过给var加{{}}但无效
  dat %>%
    group_by({{by}}) %>%   
    dplyr::summarise(mean=list(smean.cl.boot({{var}}, conf.int=conf.int))) %>%
    unnest_wider(mean)
}
ci_boot(dat = x, by = wk, var = pd)

错误原因 #

你直接使用is.numeric(var)时，检查的是符号var本身，而非数据框dat中对应的列。函数调用时传入的pd是一个未在全局环境定义的符号，R无法找到这个对象，因此抛出“object 'pd' not found”的错误。

要正确判断输入列的类型，需要先从数据框中提取出指定列，再进行数值型检查。

修正后的代码 #

ci_boot <- function(dat, by, var, conf.int = 0.90,...) {
  # 从数据框中提取指定列，再检查是否为数值型
  if(!is.numeric(pull(dat, {{var}}))) {
    stop("'var' must be numeric")
  }  
  dat %>%
    group_by({{by}}) %>%   
    dplyr::summarise(mean=list(smean.cl.boot({{var}}, conf.int=conf.int))) %>%
    unnest_wider(mean)
}

# 测试数值列（正常执行）
ci_boot(dat = x, by = wk, var = pd)

# 测试文本列（触发错误提示）
ci_boot(dat = x, by = wk, var = test)

这里用pull(dat, {{var}})从数据框中提取用户指定的列，再用is.numeric判断类型，既实现了数值检查的逻辑，又避免了符号找不到的问题。

内容的提问来源于stack exchange，提问作者Salvador