A comparison of apples and oranges occurs when two items or groups of items are compared that cannot be practically compared.
The idiom, comparing apples and oranges, refers to the apparent differences between items which are popularly thought to be incomparable or incommensurable, such as apples and oranges. The idiom may also be used to indicate that a false analogy has been made between two items, such as where an apple is faulted for not being a good orange.
Variants
The idiom is not unique. In Quebec French, it may take the form comparer des pommes avec des oranges, while in European French the idiom says comparer des pommes et des poires . In Latin American Spanish, it is usually comparar papas y boniatos  or comparar peras con manzanas . In some other languages the term for orange derives from apple, suggesting not only that a direct comparison between the two is possible, but that it is implicitly present in their names. Fruit other than apples and oranges can also be compared; for example, apples and pears are compared in Danish, Dutch, German, Spanish, Swedish, Croatian, Czech, Romanian, Hungarian, Italian, Slovene, Luxembourgish, Bosnian, and Turkish. However, apples are actually more closely related to pears  than to oranges. In fact, in the Spanish-speaking world, a common idiom is sumar peras con manzanas, that is, to add pears and apples; the same thing applies in Italian and Romanian, where popular idioms are respectively sommare la mele con le pere and a aduna merele cu perele. In Czech language the idiom míchat jablka s hruškami literally means to mix apples and pears.
Some languages use completely different items, such as the Serbian Поредити бабе и жабе, or the Romanian baba şi mitraliera ; vaca şi izmenele ; or țiganul şi carioca, or the Welsh mor wahanol â mêl a menyn, while some languages compare dissimilar properties of dissimilar items. For example, an equivalent Danish idiom, Hvad er højest, Rundetårn eller et tordenskrald? translates literally as What is highest, the Round Tower or a thunderclap?, referring to the size of the former and the sound of the latter. In Russian, the phrase сравнивать тёплое с мягким  is used. In British English, the phrase chalk and cheese means the same thing as apples and oranges. In Argentina, a common question is ¿En qué se parecen el amor y el ojo del hacha? which translates into What do love and the eye of an axe have in common? and emphasizes dissimilarity between two subjects; in Colombia, a similar  version is common: confundir la mierda con la pomada, literally, to confuse shit with salve. In Polish, the expression co ma piernik do wiatraka? is used, meaning What has  gingerbread to a windmill?. In Chinese, a phrase that has the similar meaning is 风马牛不相及, literally meaning "horses and cattles won't cross into each other's area", and later used to describe things that are totally unrelated and incomparable.
A number of more exaggerated comparisons are sometimes made, in cases in which the speaker believes the two objects being compared are radically different beyond reproach. For example "oranges with orangutans", "apples with dishwashers", and so on. In English, different fruits, such as pears, plums, or lemons are sometimes substituted for oranges in this context.
Sometimes the two words sound similar, for example, Romanian merele cu perele  and the Hungarian szezont a fazonnal .
A Hungarian expression with a somewhat modified meaning and construction is ízlések és pofonok . It refers to the fact that you cannot decide which one is better from things that depend only on the different tastes/preferences of people, just as you cannot compare two slaps in the face if they are received by separate people.
Further, the phrase "apples-with-apples comparison" is used when an attempt is made to make sure that the comparison is fair; for example, adjusting for inflation during a discussion of wages.
Criticism of the idiom
Various scholars have questioned the premise of the incomparable nature of apples and oranges, both in serious publications and in weblogs and spoofs . These criticisms of the idiom, however, tend to assume that you cannot compare apples and oranges is a descriptive statement capable of logical or scientific counter-example, without addressing the possibility of interpreting the idiom as a normative statement .
Scientific
At least two to