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The R Inferno
Patrick Burns1 30th April 2011

1 This document resides in the tutorial section of http://www.burns-stat.com. More elementary material on R may also be found there. S+ is a registered trademark of TIBCO Software Inc. The author thanks D. Alighieri for useful comments.

Contents
Contents List of Figures List of Tables 1 Falling into the Floating Point Trap 2 Growing Objects 16 7 9 12

3 Failing to Vectorize 17 3.1 Subscripting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 3.2 Vectorized if . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 3.3 Vectorization impossible . . . . . . . . . . . . . . . . . . . . . . . 22 4 Over-Vectorizing 5 Not 5.1 5.2 5.3 24

Writing Functions 27 Abstraction . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . 27 Simplicity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Consistency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 35 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 38 39 39 40 40 40 41 42 42

6 Doing Global Assignments 7 Tripping on Object Orientation 7.1 S3 methods . . . . . . . . . . . 7.1.1 generic functions . . . . 7.1.2 methods . . . . . . . . . 7.1.3 inheritance . . . . . . . 7.2 S4 methods . . . . . . . . . . . 7.2.1 multiple dispatch .. . . 7.2.2 S4 structure . . . . . . . 7.2.3 discussion . . . . . . . . 7.3 Namespaces . . . . . . . . . . .

1

CONTENTS 8 Believing It Does as Intended 8.1 Ghosts . . . . . . . . . . . . . . . . . . . . . . 8.1.1 differences with S+ . . . . . . . . . . . 8.1.2 package functionality . . . . . . . . . . 8.1.3 precedence . . . . . . . . . . . . . . . 8.1.4 equality of missing values . . . . .. . 8.1.5 testing NULL . . . . . . . . . . . . . . 8.1.6 membership . . . . . . . . . . . . . . . 8.1.7 multiple tests . . . . . . . . . . . . . . 8.1.8 coercion . . . . . . . . . . . . . . . . . 8.1.9 comparison under coercion . . . . . . 8.1.10 parentheses in the right places . . . . 8.1.11 excluding named items . . . . . . . . . 8.1.12 excluding missing values . . . . . . . . 8.1.13 negativenothing is something . . . . . 8.1.14 but zero can be nothing . . . . . . . . 8.1.15 something plus nothing is nothing . . 8.1.16 sum of nothing is zero . . . . . . . . . 8.1.17 the methods shuffle . . . . . . . . . . . 8.1.18 first match only . . . . . . . . . . . . . 8.1.19 first match only (reprise) . . . . . . . 8.1.20 partial matching can partially confuse 8.1.21 no partial match assignments . . .. . 8.1.22 cat versus print . . . . . . . . . . . . . 8.1.23 backslashes . . . . . . . . . . . . . . . 8.1.24 internationalization . . . . . . . . . . . 8.1.25 paths in Windows . . . . . . . . . . . 8.1.26 quotes . . . . . . . . . . . . . . . . . . 8.1.27 backquotes . . . . . . . . . . . . . . . 8.1.28 disappearing attributes . . . . . . . . 8.1.29 disappearing attributes (reprise) . . . 8.1.30when space matters . . . . . . . . . . 8.1.31 multiple comparisons . . . . . . . . . . 8.1.32 name masking . . . . . . . . . . . . . 8.1.33 more sorting than sort . . . . . . . . . 8.1.34 sort.list not for lists . . . . . . . . . . 8.1.35 search list shuffle . . . . . . . . . . . . 8.1.36 source versus attach or load . . . . . . 8.1.37 string not the name . . . . . . . . . . 8.1.38 get a component . .. . . . . . . . . . 8.1.39 string not the name (encore) . . . . . 8.1.40 string not the name (yet again) . . . . 8.1.41 string not the name (still) . . . . . . . 8.1.42 name not the argument . . . . . . . . 8.1.43 unexpected else . . . . . . . . . . . . . 8.1.44 dropping dimensions . . . . . . . . . . 2

CONTENTS 44 46 46 46 47 48 48 49 49 50 51 51 51 52 52 53 53 54 54 55 55 56 58 58 59 59 60...
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