[R] Why do data frame column types vary across apply, lapply?

[Jeff Brown]

Hi, 

I still have little ability to predict how these functions will treat the
columns of data frames:

> # Here's a data frame with a column "a" of integers, 
> # and a column "b" of characters: 
> df <- data.frame( 
+ a = 1:2, 
+ b = c("a","b") 
+ ) 
> df 
  a b 
1 1 a 
2 2 b 
> 
> # Except -- both columns are characters: 
> apply (df, 2, typeof) 
          a           b 
"character" "character" 
> 
> # Except -- they're both integers: 
> lapply (df, typeof) 
$a 
[1] "integer" 

$b 
[1] "integer" 

> 
> # Except -- only one of those integers is numeric: 
> lapply (df, is.numeric) 
$a 
[1] TRUE 

$b 
[1] FALSE 


Many thanks,
Jeff
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