[Rd] unique.matrix issue [Was: Anomaly with unique and match]

From: Simon Urbanek <simon.urbanek_at_r-project.org>
Date: Wed, 09 Mar 2011 14:11:49 -0500

match() is a red herring here -- it is really a very specific thing that has to do with the fact that you're running unique() on a matrix. Also it's much easier to reproduce:

> x=c(1,1+0.2e-15)
> x

[1] 1 1
> sprintf("%a",x)

[1] "0x1p+0" "0x1.0000000000001p+0"
> unique(x)

[1] 1 1
> sprintf("%a",unique(x))

[1] "0x1p+0" "0x1.0000000000001p+0"
> unique(matrix(x,2))

     [,1]
[1,] 1  

and this comes from the fact that unique.matrix uses string representation since it has to take into account all values of a row/column so it pastes all values into one string, but for the two numbers that is the same:
> as.character(x)

[1] "1" "1"

Cheers,
Simon

On Mar 9, 2011, at 9:48 AM, Terry Therneau wrote:

> I stumbled onto this working on an update to coxph. The last 6 lines
> below are the question, the rest create a test data set.
>
> tmt585% R
> R version 2.12.2 (2011-02-25)
> Copyright (C) 2011 The R Foundation for Statistical Computing
> ISBN 3-900051-07-0
> Platform: x86_64-unknown-linux-gnu (64-bit)
>
> # Lines of code from survival/tests/singtest.R

>> library(survival)

> Loading required package: splines
>> test1 <- data.frame(time=  c(4, 3,1,1,2,2,3),

> + status=c(1,NA,1,0,1,1,0),
> + x= c(0, 2,1,1,1,0,0))
>> >> temp <- rep(0:3, rep(7,4)) >> >> stest <- data.frame(start = 10*temp,
> + stop = 10*temp + test1$time,
> + status = rep(test1$status,4),
> + x = c(test1$x+ 1:7, rep(test1$x,3)),
> + epoch = rep(1:4, rep(7,4)))
>> >> fit1 <- coxph(Surv(start, stop, status) ~ x * factor(epoch), stest)

>
> ## New lines
>> temp1 <- fit1$linear.predictor
>> temp2 <- as.matrix(temp1)
>> match(temp1, unique(temp1))

> [1] 1 2 3 4 4 5 6 7 7 7 6 6 6 8 8 8 6 6 6 9 9 9 6 6
>> match(temp2, unique(temp2))

> [1] 1 2 3 4 4 5 6 7 7 7 6 6 6 NA NA NA 6 6 6 8 8 8
> 6 6
>
> -----------------------
>
> I've solved it for my code by not calling match on a 1 column vector.
> In general, however, should I be using some other paradym for this "map
> to unique" operation? For example match(as.character(x),
> unique(as.character(x)) ?
>
> Terry T
>
> ______________________________________________
> R-devel_at_r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>
>


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