Numbers that look equal, should be equal, but if() doesn'tsee as equal (repost with code included)

Try the following function (the name is supposed to be a joke, by the
way),
which will also do the right thing with NAs and characters. Use it as
if(equal.enough(x,y)) rather than if(x==y), e.g.

equal.enough(0.1+0.2, 0.3)

[1] TRUE

My default of 15 significant figures may be overkill in many
applications; be
prepared to reduce this.

Simon Fear


"equal.enough" <- function(x, y, sig.figs=15, d.p.zero=-Inf) {
# set argument d.p.zero to a real but small number (e.g. 1e-15) to
overide
# the sig.figs setting in favour of decimal places for comparison of
extremely small numbers
# (if appropriate - which is not always the case)
	if (is.numeric(x)) {
	  if (is.numeric(y)) {
	    if (is.infinite(d.p.zero))
		ifelse(is.na(x), is.na(y),
		ifelse(is.na(y), F,
		abs(signif(x, sig.figs) - signif(y, sig.figs)) == 0))
	    else
		ifelse(is.na(x), is.na(y),
		ifelse(is.na(y), F,
		abs(signif(x, sig.figs) - signif(y, sig.figs)) <=
d.p.zero))
	  } 
	  else is.na(y)		# a vector of F as long as y
	} else x==y
}
 

Simon Fear
Senior Statistician
Syne qua non Ltd
Tel: +44 (0) 1379 644449
Fax: +44 (0) 1379 644445
email: Simon.Fear at synequanon.com
web: http://www.synequanon.com
 
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