R，使用包含grepl（）的ifelse的dplyr :: mutate会产生意外结果(R, using dplyr::mutate with ifelse containing a grepl() gives unexpected result)

 这个ifelse声明有什么问题。 
 
df <- data.frame(var1=c('ABC','CAB', 'AB'))
dplyr::mutate(df, var2=ifelse(grepl('^AB',var1), 'AB-starter', var1))
 
 给 
 
  var1       var2
1  ABC AB-starter
2  CAB          3
3   AB AB-starter
 
 我想（使用mutate和ifelse语句）var2的第二个元素中var1的值（即'var1'不以“AB”开头）： 
 
  var1       var2
1  ABC AB-starter
2  CAB        CAB
3   AB AB-starter

What is wrong with this ifelse statement. 
 
df <- data.frame(var1=c('ABC','CAB', 'AB'))
dplyr::mutate(df, var2=ifelse(grepl('^AB',var1), 'AB-starter', var1))
 
Gives 
 
  var1       var2
1  ABC AB-starter
2  CAB          3
3   AB AB-starter
 
I wanted (using mutate and a ifelse statement) the value of var1 in second element of var2 (that is when 'var1' does not start with "AB"):
 
  var1       var2
1  ABC AB-starter
2  CAB        CAB
3   AB AB-starter

原文：https://stackoverflow.com/questions/40043962