r - Why doesn't comparison between numeric and character variables give a warning?

Question

I had a bug in my code resulting from an inadvertent comparison between a character variable and a numeric variable (they were both supposed to be numeric). This bug would have been much easier to find if R had a warning when doing this type of comparison. For example, why does this not throw a warning

> 'two' < 5
[1] FALSE

but this does throw a warning

> as.numeric('two') < 5
[1] NA
Warning message:
NAs introduced by coercion 

It is not clear to me what is going on behind the scenes in the first comparison?

Answer 1

In your example 5 is converted to a character, so the test is the same as 'two' < as.character(5).

From ?Comparison:

If the two arguments are atomic vectors of different types, one is coerced to the type of the other, the (decreasing) order of precedence being character, complex, numeric, integer, logical and raw.