[R] sensitivity logical operators in R

Marc Jekel feuerwald at gmx.de
Sun Jan 23 23:13:11 CET 2011

Hello R Fans,

Another question for the community that really frightened me today. The 
following logical comparison produces a "false" as output:

t = sum((c(.7,.69,.68,.67,.66)-.5)*c(1,1,-1,-1,1))
tt = sum((c(.7,.69,.68,.67,.66)-.5)*c(1,-1,1,1,-1))

t == tt

This is really strange behavior. Most likely this has something to do 
how R represents numbers internally and the possible sensitivity of a 
computer? Does anyone know when this strange behavior occurs and how to 
fix it?

Thank you all! This list is pleasure!!!


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