How do I correctly handle NA coercion warning

0
votes

I want to cast a column from character to numeric. Some values cannot be cast. This results in a warning, which is expected behavior.

data.frame(a=c("5","7","not_a_number"),stringsAsFactors = F) %>% mutate(value=as.numeric(a))

Additionally I have another column giving me the information, which rows can be cast to numeric (logical). I want to use this column so that R can be sure that it doesn't have to coerce.

data.frame(a=c("5","7","not_a_number"),b=c(1,1,0),stringsAsFactors = F) %>% 
mutate(value=ifelse(b,as.numeric(a),NA_integer_))

But this gives the same error. Why? Nothing should be coerced here. I am handling and responsible for the correct and compatible type across the rows. What is happening?

2
rdplyrcoercion

2 Answers

2
votes

You need to apply as.numeric outside of ifelse :

library(dplyr)
df %>% mutate(value = as.numeric(ifelse(b,a,NA)))

#             a b value
#1            5 1     5
#2            7 1     7
#3 not_a_number 0  <NA>

where df is :

df <- data.frame(a=c("5","7","not_a_number"),b=c(1,1,0),stringsAsFactors = FALSE)
0
votes

Indirect answer, why not remove all non-digits before converting to a numeric:

data.frame(a = c("5","7","not_a_number"), stringsAsFactors = FALSE) %>%
  mutate(value = as.numeric(gsub("\\D+", "", a)))
#              a value
# 1            5     5
# 2            7     7
# 3 not_a_number    NA