Deloitte Interview Questions | What is the output for the below expression all(NA==NA)?

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R

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TheDataMonk 55 years 3 Answers 1189 views Grand Master 0

Answers ( 3 )

  1. Missing values (NA) and NaN values are regarded as non-comparable even to themselves,
    so comparisons involving them will always result in NA.

  2. NA is identical to NA, but doesn’t equal it. If you run NA==NA, the response will be NA, because the equal operator doesn’t apply to NAs. From the identical documentation:

    A call to identical is the way to test exact equality in if and while statements, as well as in logical expressions that use && or ||. In all these applications you need to be assured of getting a single logical value.

    Users often use the comparison operators, such as == or !=, in these situations. It looks natural, but it is not what these operators are designed to do in R. They return an object like the arguments. If you expected x and y to be of length 1, but it happened that one of them was not, you will not get a single FALSE. Similarly, if one of the arguments is NA, the result is also NA. In either case, the expression if(x == y)…. won’t work as expected.

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