Why does identical() return FALSE for what are obviously the same objects?-CodePudding

I do not understand the following code. Why are the following two objects not identical?

a <- dim(matrix(nrow=1, ncol=1)); a
# [1] 1 1
identical(a, c(1,1))
# FALSE

CodePudding user response：

Because dim returns an integer vector. However, c(1, 1) is a floating point vector. Unfortunately the difference can’t be seen simply by printing their values but you can inspect the class of the values, which will show as integer and numeric (= floating point numbers), respectively.

To get the same result, do the following:

identical(a, c(1L, 1L))
# [1] TRUE

CodePudding user response：

When you type ?identical, you will see

The safe and reliable way to test two objects for being exactly equal. It returns TRUE in this case, FALSE in every other case.

However, c(1,1) gives a numeric array, but dim returns the integer one, which is not exactly the same class.

You can try all.equal, which checks the "near equality", e.g.,

> all.equal(a,c(1,1)) 
[1] TRUE