Comparisons of floating point numbers are problematic due to errors associated with the binary representation of decimal numbers. Computer scientists and programmers are aware of these problems [.e.g., @Goldberg:1991ac] and yet people still use numerical methods which fail to account for floating point errors (this pitfall is the first to be highlighted in the First Circle of “The R Inferno” [@Burns:2012ri]).
To avoid these and other numerical rounding issues, R's help file for relational operators (e.g., ?'>') suggests using identical and all.equal when making numerical comparisons:
x1 <- 0.5 - 0.3
x2 <- 0.3 - 0.1
x1 == x2 # FALSE on most machines
identical(all.equal(x1, x2), TRUE) # TRUE everywhere
Inspired by R FAQ 7.31 and this Stack Overflow answer, this package provides new relational operators useful for performing floating point number comparisons with a set tolerance:
fpCompare[1] |
base |
|---|---|
%>=% |
>= |
%>>% |
> |
%<=% |
<= |
%<<% |
< |
%==% |
== |
%!=% |
!= |
These functions use the base relational operators to make comparisons, but incorporate a tolerance value (fpCompare.tolerance) similar to all.equal. The default fpCompare.tolerance value is .Machine$double.eps^0.5, set via options. This is the same default used in all.equal for numeric comparisons.
# set telorance value
tol = .Machine$double.eps^0.5 # default value
options(fpCompare.tolerance = tol)
# perform comparisons
x1 <- 0.5 - 0.3
x2 <- 0.3 - 0.1
x1 == x2 # FALSE on most machines
x1 %==% x2 # TRUE everywhere
[1]: The %<<% and %>>% symbols are used instead of %<% and %>% to avoid a conflict with magrittr's pipe operator (%>%).
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install.packages("fpCompare")
library(devtools)
install_github("achubaty/fpCompare")
https://github.com/PredictiveEcology/fpCompare/issues