Chris -
If you check the documentation for the "$" operator,
for example by typing
help("$")
you'll find (among a lot of other information):
name: A literal character string or a name (possibly backtick
quoted). For extraction, this is normally (see under
‘Environments’) partially matched to the ‘names’ of the
object.
So when you use the "$" operator (but not "[" or "[["), partial
matching is performed. For example:
x = data.frame(PHQ9=1:10)
x$PHQ
[1] 1 2 3 4 5 6 7 8 9 10
x[,'PHQ']
Error in `[.data.frame`(x, , "PHQ") : undefined columns selected
x[['PHQ']]
NULL
So if you don't want this "feature", you can use brackets instead
of the dollar sign for extraction.
- Phil Spector
Statistical Computing Facility
Department of Statistics
UC Berkeley
spec...@stat.berkeley.edu
On Sun, 29 May 2011, Chris Evans wrote:
I may be being dopey, I surely am, but I'm baffled by this. I've been
working, on and off for a few days in R version 2.13.0 (2011-04-13)
i386-pc-mingw32/i386 (32-bit) working it through ESS.
I've got a dataframe created a couple of days back, during the session:
dim(AllDat)
[1] 27270 94
I came back this morning and misremembered my variables and thought I
had a variable AllDat$PHQ and started using it and everything seemed
fine until I realised that I shouldn't have it (!) and that the variable
I was thinking of is AllDat$PHQ9 and that's there:
colnames(AllDat)[grep("PHQ",colnames(AllDat))]
[1] "PHQ9" "HasPHQ" "ZeroPHQ"
and, as you can see, AllDat$PHQ. But I can I do:
head(table(AllDat$PHQ))
0 1 2 3 4 5
731 527 764 845 872 915
Ooops ... so AllDat$PHQ _DOES_ exist. Its contents exactly match
AllDat$PHQ9:
table(abs(AllDat$PHQ - AllDat$PHQ9))
0
19032
I have searched back through my ESS transcript back to the start of the
session and I can't see anywhere I've assigned to AllDat$PHQ (and I've
never used "attach").
However, I guess that somehow I must have managed to duplicate AllDat in
more than one open environment so I check out and I have 16 environments
(I'm sure that's not right terminology, apologies):
search()
[1] ".GlobalEnv" "package:reshape2"
[3] "package:Hmisc" "package:survival"
[5] "package:splines" "package:nnet"
[7] "package:MASS" "package:gdata"
[9] "package:stats" "package:graphics"
[11] "package:grDevices" "package:utils"
[13] "package:datasets" "package:methods"
[15] "Autoloads" "package:base"
So I try:
for (i in 1:16) { print(paste("i =",i,exists("AllDat",i,inherits =
FALSE))) }
[1] "i = 1 TRUE"
[1] "i = 2 FALSE"
[1] "i = 3 FALSE"
[1] "i = 4 FALSE"
[1] "i = 5 FALSE"
[1] "i = 6 FALSE"
[1] "i = 7 FALSE"
[1] "i = 8 FALSE"
[1] "i = 9 FALSE"
[1] "i = 10 FALSE"
[1] "i = 11 FALSE"
[1] "i = 12 FALSE"
[1] "i = 13 FALSE"
[1] "i = 14 FALSE"
[1] "i = 15 FALSE"
[1] "i = 16 FALSE"
So I don't think I do have two different AllDat dataframes.
Can anyone throw light on what's going on? I have searched archives
etc. but can't think of sensible keywords and so far turned up nothing.
Happy to be told RTFM or the equivalent but could someone point me to a
specific location? Also happy to try any diagnostics anyone recommends.
Many thanks in advance,
Chris
--
Chris Evans <ch...@psyctc.org> Skype: chris-psyctc
Consultant Psychiatrist in Psychotherapy, Notts. PDD network;
Professor, Psychotherapy, Nottingham University
*If I am writing from one of those roles, it will be clear. Otherwise*
*my views are my own and not representative of those institutions *
If you have difficulty Emailing me on this address or getting a reply,
send again but cc to: chris dot evans at nottshc dot nhs dot uk
and to: c dot evans at nottingham dot ac dot uk
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