# [Rd] Anomaly with unique and match

Terry Therneau therneau at mayo.edu
Wed Mar 9 15:48:10 CET 2011

```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)
> 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

```