On 2011-03-11 01:07, Ivan Calandra wrote:
Hi,
From ?"$", you can see that using [[ instead would do what you're
looking for. You should read and try to understand the whole help file.
The reason is that for [[ the default is exact=TRUE, wheareas for $ the
only possible value is exact=FALSE, which means partial matching if
possible.
So try A[["aa"]] instead.
Indeed. And, as always, shortcuts come with caveats.
Like using T/F for TRUE/FALSE, use of $ extraction
may be convenient but is best avoided unless you're
sure of its effect.
Peter Ehlers
HTH,
Ivan
Le 3/11/2011 09:55, Håvard Rue a écrit :
I had an obscure bug that boiled down to this ``feature'' in R,
Read 3921 items
A = list(aa = 1)
A
$aa
[1] 1
if (A$a) print("a is there")
[1] "a is there"
The test appear to check is A$a is TRUE, but what happen is that it
auto-complete (silently), and expand to 'A$aa'.
The problem was caused by the fact that I had also a element named 'a'
which was evaluated to NULL, like
A$a = NULL
A
$aa
[1] 1
if (A$a) print("a is there")
[1] "a is there"
since NULL elements are removed from the list, and that A$a auto-expand
to A$aa, my error appeared.
To me, this seems not a feature I want in order to have a robust
program.
Is there any option to turn this ''feature'' off?
Best,
H
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