First circle of R hell. 0.1 != 0.3/3

Question

Possible Duplicate:
Numeric comparison difficulty in R

Hello All,

According to "R Inferno" paper. I'm right now in the first circle of R hell. This is where pagans expect 0.1 == 0.3/3. Paper recommends using all.equal function for such cases, however I need to check ">=" or "<=" conditions. With current example on of them fail:

> .1 >= .3/3
[1] TRUE
> .1 <= .3/3
[1] FALSE

Is there a similar function to all.equal that checks inequalities?

Thank you,

Ilya

That's not an R specific error, but a common error that is caused by the binary representation of floating point numbers. See http://en.wikipedia.org/wiki/Floating_point#Accuracy_problems for example. — schnaader, Nov 02 '10 at 15:17
I know why error occurs. I would like to know if there is a R function that can check inequalities or I need to write one with floating points in mind. — ilya, Nov 02 '10 at 15:22

score 10 · Answer 1 · answered Nov 02 '10 at 15:30

The main test of all.equal is whether abs(x-y) < tolerance for some values x and y and some small tolerance. Equivalent inequality tests would check:

x <= y:         x-y < tolerance
x < y:          x-y < -tolerance
x >= y:         x-y > -tolerance
x > y:          x-y > tolerance

score 9 · Accepted Answer · edited May 23 '17 at 11:45

9

See these questions:

Generally speaking, you can deal with this by including a tolerance level as per the second link above.

edited May 23 '17 at 11:45

Community

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answered Nov 02 '10 at 15:26

Shane

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See the second link which directly answers the question. – Shane Nov 02 '10 at 15:27
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Thank you Shane, in second link I found your post with creating new operator - exactly what I wanted. Thank you!! – ilya Nov 02 '10 at 15:47
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Duplicate identification belongs in the comments. – dmckee --- ex-moderator kitten Nov 02 '10 at 18:22
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Thanks for the advice, @dmckee. I had made a comment to that effect. – Shane Nov 02 '10 at 18:27

score 6 · Answer 3 · answered Nov 02 '10 at 15:20

6

Please see the R FAQ entry Why doesn't R think these numbers are equal and the references therein.

answered Nov 02 '10 at 15:20

Dirk Eddelbuettel

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This is fascinating, but not an answer to the OP. – mob Nov 02 '10 at 15:24
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Sure is, or you read another entry 7.31. The example there is `sqrt(2)*sqrt(2) == 2` comes out as FALSE and is the same issue here: representation of floating point numbers. – Dirk Eddelbuettel Nov 02 '10 at 15:28

score 4 · Answer 4 · answered Nov 02 '10 at 15:28

4

You could try judicious use of zapsmall() which seems to give the behavior you are looking for. I don't know if this works in all situations. e.g.,

.1 >= zapsmall(.3/3)
[1] TRUE
> .1 <= zapsmall(.3/3)
[1] TRUE

answered Nov 02 '10 at 15:28

kmm

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First circle of R hell. 0.1 != 0.3/3

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