Anonymous function in R not returning expected output

Question

I have this dataframe:

df <- data.frame(c(NA,2,3,1),c(4,NA,6,1),c(7,8,NA,9),c(1,5,6,4))
colnames(df) <- c('x1','x2','x3','x4')`

If I write a simple imputation function that imputes NA values as such:

impute <- function(x, imputation.method) { 
x[is.na(a)] <- imputation.method
x
}

And call it on the first two columns in the original dataframe. It imputes the NA values properly as such:

library(purrr)
df[,c('x1', 'x2')] <- map(df[,c('x1', 'x2')], impute, 0)
df

# x1 x2 x3 x4    
# 0  4  7  1     
# 2  0  8  5     
# 3  6 NA  6    
# 1  1  9  4

Then if I try to do it in a one-liner using an anonymous function it returns the following undesired output:

df[,c('x1', 'x2')] <- map(df[,c('x1', 'x2')], function(x){x[is.na(x)] <- 0 })

# x1 x2 x3 x4    
# 0  0  7  1     
# 0  0  8  5     
# 0  0 NA  6    
# 0  0  9  4

I am unaware as to why rewriting my original function the same as a one-line anonymous function changes the output. Any input as to why this is occurring and how change the anonymous function to return the desired output is appreciated!

moodymudskipper · Accepted Answer · 2018-07-31 23:06:40Z

3

There you go!

  df[,c('x1', 'x2')] <- map(df[,c('x1', 'x2')], function(x){x[is.na(x)] <- 0;x })
  #   x1 x2 x3 x4
  # 1  0  4  7  1
  # 2  2  0  8  5
  # 3  3  6 NA  6
  # 4  1  1  9  4

your function was returning 0, it needs to return the modified x

Here's another way to write it:

mutate_at(df, c('x1', 'x2'), ~`[<-`(., is.na(.), value = 0))

answered Jul 31, 2018 at 23:06

moodymudskipper

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2 Comments

Michael Over a year ago

Awesome! So every time I write an anonymous function I need to return x just as I would a normal function? Does the ; in the anonymous function create a line break? If not, what purpose does it serve here?

moodymudskipper Over a year ago

a function, anonymous or not, returns the latest evaluation (when you don't use return). ; is indeed like a line break. Here, though you were modifying x, you were assigning 0, so that's what was returned. It's a common mistake (that i make occasionally :) ).

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