1
general::
Unlike objects or persons, as in Assessing the problems of the neighborhood grocery by examining a giant supermarket is comparing apples and oranges. This metaphor for dissimilarity began as applesand oysters, which appeared in John Ray's proverb collection of 1670. It is nearly always accompanied by a warning that one cannot compare such different categories.
American Heritage Idioms
2
general::
Phrase(s): apples and oranges
Fig. two entities that are not similar. (Used especially in reference to comparisons of unlike things.) • You can’t talk about Fred and Ted in the same breath! They’re like apples and oranges. • Talking about her current book and her previous bestseller is like comparing apples and oranges.
McGrawhill's American Idioms And Phrasal Verbs