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

[Simon Urbanek]

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
> 
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