[Rd] Anomaly with unique and match

From: Terry Therneau <therneau_at_mayo.edu>
Date: Wed, 09 Mar 2011 08:48:10 -0600


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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