How to use quotation API to implement inplace mutate helper?

[holger brandl]

Hi,

I'm exploring the quotation API to write custom verbs. My idea is to streamline column transforms within a pipe. So I'd love to inline 

iris$Species %<>% str_replace("vir", "foo")

into a piped chain. I know I could do

iris %>% mutate(Species = Species %>% str_replace("vir", "foo"))

but to make it more concise I'd rather like to write just

iris %>% mutate_inplace(Species, str_replace("vir", "foo"))

which I have tried to implement as

mutate_inplace = function(df, variable, expr){
    quoVar <- enquo(variable)
    varName = quo_name(quoVar)

    mutate(df, !!varName :=  quoVar %>% !!enquo(expr))
}

However this fails with the error:

Error in mutate_impl(.data, dots) : 

  Column `Species` is of unsupported type quoted call

What am I doing wrong here?

Thanks,

best,

Holger

[Romain Francois]

Hello, 

That sounds like a job for mutate_at 

iris %>% mutate_at("Species", funs(str_replace(., "vir", "foo")))

Otherwise, I have something close to your example, using enexpr instead of enquo, I could not make quosures and pipes interact nicely: 

mutate_inplace <- function(data, var, expr ){

  var      <- enexpr(var)

  var_name <- quo_name(var) 

  expr <- enexpr(expr)

  call <- quo( UQ(var) %>% UQ(expr) )

  print(call)

  mutate( data, !!var_name := UQ(call) )

}

mutate_inplace( iris, Species, str_replace("vir", "foo") )

Romain

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[Holger Brandl]

Thanks Romain, works perfectly!

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