How can I use apply properly in R in this dataframe column? - r

Question

I have a dataframe column with NA, I want to how can I use apply (or lapply, sapply, ...) to the column.
I've tried with apply and lapply, but it return an error.
The function I want to apply to the column is:
a.b <- function(x, y = 165){
if (x < y)
return('Good')
else if (x > y)
return('Bad')
}
the column of the dataframe is:
data$col = 180 170 NA NA 185 185
When I use apply I get:
apply(data$col, 2, a.b)
Error in apply(data$col, 2, a.b) :
dim(X) must have a positive length
I have try dim(data$col) and the return is NULL and I think it is because of the NA's.
I also use lapply and I get:
lapply(data$col, a.b)
Error in if (x < y) return("Good") else if (x > y) return("Bad") :
missing value where TRUE/FALSE needed
This is for a course of R for beginners that I am doing so I am sorry if I made some mistakes. Thanks for taking your time to read it and trying to help.

Answer 1

apply is used on a matrix, not a vector. Try:
a.b <- function(x, y = 165){
if (is.na(x)){
return("NA")
} else if (x < y){
return('Good')} else if (x > y){
return('Bad')}
}
data$col=sapply(data$col,a.b)

Answer 2

You should be able to solve this with mapply by specifying the values to pass into your parameters:
mapply(a.b, x = data[,'col'], y = 165)
Note that you may need to modify your a.b.() function in order to manage the NA's.

Answer 3

There's a few issues going on here:
apply is meant to run on a something with a dimension to act over, which is the MARGIN argument. A column, which you're passing to apply has no dimension. see below:
> dim(mtcars)
[1] 32 11
> dim(mtcars$cyl)
NULL
apply and lapply are meant to run over all columns (or rows if you're using that margin for apply). If you want to just replace one column, you should not use apply. Do something like data$my_col <- my_func(data$my_col) if you want to replace my_col with the result of passing it to my_func
NA values do not return TRUE or FALSE when using an operator on them. Note that 7 < NA will return NA. Your if statement is looking for a TRUE or FALSE value but getting an NA value, hence the error in your second attempt. If you want to handle NA values, you may need to incorporate that into your function with is.na.
Your function should be vectorized. See circle 3 of the R-Inferno. Currently, it will just return length 1 vectors of "Good" or "Bad". My hunch is what you want is similar to the following (although not exactly same if x == y)
a.b <- function(x, y = 165){
ifelse(x < y, "Good", "Bad")
}
I beleive using the above info should get you where you want to be.