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 and yet people still use numerical methods which fail to account for floating point errors (this pitfall is the first to be highlighted in Circle 1 of Burns (2012) The R Inferno).
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 everywhereInspired 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:
fpCompare1 |
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 everywhereinstall.packages("fpCompare")library(devtools)
install_github("PredictiveEcology/fpCompare")https://github.com/PredictiveEcology/fpCompare/issues
The %<<% and
%>>% symbols are used instead of %<%
and %>% to avoid a conflict with magrittr’s
pipe operator (%>%).↩︎