R: Why does "ifelse" coerce factor into integer? -


this question has answer here:

i'm attempting change values of variable na values if they're not in vector:

sample <- factor(c('01', '014', '1', '14', '24')) df <- data.frame(var1 = 1:6, var2 = factor(c('01', '24', 'none', '1', 'unknown', '24'))) df$var2 <- ifelse(df$var2 %in% sample, df$var2, na)

for reason r not preserve original values of factor variable turns them numeric sequence:

> sample <- factor(c('01', '014', '1', '14', '24')) > df <- data.frame(var1 = 1:6,                     var2 = factor(c('01', '24', 'none', '1', 'unknown', '24'))) > class(df$var2) [1] "factor" > df   var1    var2 1    1      01 2    2      24 3    3    none 4    4       1 5    5 unknown 6    6      24 > df$var2 <- ifelse(df$var2 %in% sample, df$var2, na) > class(df$var2) [1] "integer" > df   var1 var2 1    1    1 2    2    3 3    3   na 4    4    2 5    5   na 6    6    3

why happen , correct way of achieving i'm trying here?

(i need use factors rather integers in order not confuse "01" , "1" , original data set large, using factors rather characters should save me memory)

i think 1 way achieve trying change levels of factor: 

levels(df$var2)[!levels(df$var2) %in% sample] <- na

by changing levels values not matching these levels converted factor na , result be:

df   var1 var2 1    1   01 2    2   24 3    3 <na> 4    4    1 5    5 <na> 6    6   24  > df$var2 [1] 01   24   <na> 1    <na> 24   levels: 01 1 24

the unknown , none values no longer in factor levels. or if keep unknown , none in values try this:

df$var2[!df$var2 %in% sample] <- na  > df   var1 var2 1    1   01 2    2   24 3    3 <na> 4    4    1 5    5 <na> 6    6   24   > df$var2 [1] 01   24   <na> 1    <na> 24   levels: 01 1 24 none unknown

the reason why ifelse changing class of data ifelse not maintain class. read second answer here: how prevent ifelse() turning date objects numeric objects

and last way @tchakravarty mentioned in comments use if_else dplyr!


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