From: Ivan Calandra <ivan.calandra_at_uni-hamburg.de>

Date: Mon, 07 Mar 2011 10:11:05 +0100

Date: Mon, 07 Mar 2011 10:11:05 +0100

Hi Tom,

That's once again the floating point number issue: see FAQ 7.31.
Look at this:

sum(m[161,])

[1] 1

sum(m[161,])==1

**[1] FALSE
**

sum(m[161,])-1

[1] 2.220446e-16

So 0.6+0.3+0.1 is indeed greater than 1

Try this instead:

round(sum(m[161,]))==1

**[1] TRUE
**
**HTH,
**

Ivan

Le 3/7/2011 08:08, Thomas.Salvesen_at_syngenta.com a écrit :

> I am trying to construct a data set with some sequences for example:

*>
**> a = seq(0,1,0.1)
**>
**> m = matrix(nrow = 1331, ncol = 3)
**> m[,1] = rep(a,121)
**> m[,2] = rep(a,11,each = 11)
**> m[,3] = rep(a,1,each = 121)
**>
**> I realize that there may be better ways of doing this, but this approach demonstrates the problem I'm having.
**>
**> I then want to get the sum of the rows and delete any row with a sum of greater than 1. But have a problem with rows containing any combination of the values 0.6, 0.3 and 0.1 as the sum of these is clearly 1, but a request for which rows have a sum greater than 1 will return rows with these values. Row 161 is the first row containing these values:
**>
**> [161,] 0.6 0.3 0.1
**>
**> which(rowSum(m)>1)
**>
**>> [53] 119 120 121 132 142 143 152 153 154 161 162
**> As far as I can tell this only affects combinations of 0.6, 0.3 and 0.1 (though I haven't checked every value in the matrix)
**>
**> If I try the following:
**>
**> q=rowSums(m)
**> which(q>1)
**>
**>> [53] 119 120 121 132 142 143 152 153 154 161 162
**> But if I add and subtract 1 from this:
**>
**> q=q+1
**> q=q-1
**> which(q>1)
**>
**> [53] 119 120 121 132 142 143 152 153 154 162
**>
**> What exactly is going on here? I don't have the problem with other combinations (eg 0.7, 0.2, 0.1). I assume that there is something about the data format that I don't understand, but if I make a data frame of the matrix I found the same effect.
**>
**> Any help would be great
**>
**> Tom
**>
**>
**>
**>
**>
**>
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-- Ivan CALANDRA PhD Student University of Hamburg Biozentrum Grindel und Zoologisches Museum Abt. Säugetiere Martin-Luther-King-Platz 3 D-20146 Hamburg, GERMANY +49(0)40 42838 6231 ivan.calandra_at_uni-hamburg.de ********** http://www.for771.uni-bonn.de http://webapp5.rrz.uni-hamburg.de/mammals/eng/1525_8_1.php ______________________________________________ R-help_at_r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.Received on Mon 07 Mar 2011 - 09:13:48 GMT

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