Details on Comparing Objects

Andreas Brandmaier

2026-10-20

When are two objects the same?

To assess whether results were the same across reproduction attempts, the reproducibleRchunks package stores selected results and compares them to results once they are reproduced (i.e., when the R Markdown document is rebuilt).

Object identity is either established by comparing their fingerprints, that is, by default a SHA256 fingerprint, or the actual contents of an object. To this end, the package uses all.equal() from base R which tests whether two objects are (nearly) equal. To test identity of two objects, the function identical() could be used. However, identity is usually a too restrictive test. We expect that different platforms with different processor architectures, different system libraries and so on lead to slight numerical differences in numerical results. Thus, the sameness of two objects is checked up to a certain tolerance.

For example, the following code should return TRUE in both instances:

all.equal(5, 2+3)

## [1] TRUE

identical(5, 2+3)

## [1] TRUE

The following code will, depending on the platform not yield perfect identity but should be (nearly) given the precision of the platform:

all.equal(1/1000000000*7, 0.000000007)

## [1] TRUE

identical(1/1000000000*7, 0.000000007)

## [1] FALSE

This is why the package uses all.equal() whereas the numerical precision can be set via options.

Further, when hashes are used, attributes of objects are compared in a canonical form, in which their attributes are first sorted.