Arun, thanks for the clarification -- I see I didn't read that thread fully.
--Mel.
On 2/14/2014 7:07 AM, Arunkumar Srinivasan wrote:
Melanie,
`set` modifies by reference. Yours'll make a copy.
Arun
------------------------------------------------------------------------
From: Bacou, Melanie Bacou, Melanie <mailto:[email protected]>
Reply: Bacou, Melanie [email protected] <mailto:[email protected]>
Date: February 14, 2014 at 12:52:56 PM
To: Matt Dowle [email protected] <mailto:[email protected]>,
John Laing [email protected] <mailto:[email protected]>
Subject: Re: [datatable-help] Force evaluation of first argument to [
Hi John, Matt,
In this case, why not simply using the standard data.table approach
with .SD?
fbq.cp[, lapply(.SD, function(x) ifelse(is.na(x), FALSE, x)),
.SDcols=c("foo", "bar", "qux")]
--Mel.
On 2/12/2014 2:22 PM, Matt Dowle wrote:
Ha. Yes we certainly don't hold back from making the messages as
long and as helpful as possible. If the code knows, or can know
what exactly is wrong, it's a deliberate policy to put that info
right there into the message. data.table is written by users; i.e.
we wrote it for ourselves doing real jobs. I think that may be the
root of that. If any messages could more helpful, those suggestions
are very welcome.
Matt
On 12/02/14 17:58, John Laing wrote:
Thanks, Matt! With a slight amendment that works great:
for (x in c("foo", "bar", "qux")) set(fbq, which(is.na
<http://is.na>(fbq[[x]])), x, FALSE)
Which highlights an opportunity to say that I really appreciate the
unusually helpful error messages in this package.
-John
On Wed, Feb 12, 2014 at 12:44 PM, Matt Dowle
<[email protected] <mailto:[email protected]>> wrote:
Hi John,
In examples like this I'd use set() and [[, since it's a bit
easier to write but memory efficient too.
for (x in c("foo", "bar", "qux")) set(fbq, is.na
<http://is.na>(fbq[[x]]), x, FALSE) [untested]
A downside here is one repetition of the "fbq" symbol, but can
live with that. If you have a large number of columns (and
I've been surprised just how many columns some poeple have!)
then calling set() many times has lower overhead than DT[,
:=], see ?set. Note also that [[ is base R, doesn't copy the
column and often useful to use with data.table.
Or, use get() in either i or j rather than eval().
HTH, Matt
On 12/02/14 17:24, John Laing wrote:
Let's say I merge together several data.tables such that I wind up
with lots of NAs:
require(data.table)
foo <- data.table(k=1:4, foo=TRUE, key="k")
bar <- data.table(k=3:6, bar=TRUE, key="k")
qux <- data.table(k=5:8, qux=TRUE, key="k")
fbq <- merge(merge(foo, bar, all=TRUE), qux, all=TRUE)
print(fbq)
# k foo bar qux
# 1: 1 TRUE NA NA
# 2: 2 TRUE NA NA
# 3: 3 TRUE TRUE NA
# 4: 4 TRUE TRUE NA
# 5: 5 NA TRUE TRUE
# 6: 6 NA TRUE TRUE
# 7: 7 NA NA TRUE
# 8: 8 NA NA TRUE
I want to go through those columns and turn each NA into
FALSE. I can
do this by writing code for each column:
fbq.cp <- copy(fbq)
fbq.cp[is.na <http://is.na>(foo), foo:=FALSE]
fbq.cp[is.na <http://is.na>(bar), bar:=FALSE]
fbq.cp[is.na <http://is.na>(qux), qux:=FALSE]
print(fbq.cp)
# k foo bar qux
# 1: 1 TRUE FALSE FALSE
# 2: 2 TRUE FALSE FALSE
# 3: 3 TRUE TRUE FALSE
# 4: 4 TRUE TRUE FALSE
# 5: 5 FALSE TRUE TRUE
# 6: 6 FALSE TRUE TRUE
# 7: 7 FALSE FALSE TRUE
# 8: 8 FALSE FALSE TRUE
But I can't figure out how to do it in a loop. More precisely,
I can't
figure out how to make the [ operator evaluate its first
argument in
the context of the data.table. All of these have no effect:
for (x in c("foo", "bar", "qux")) fbq[is.na <http://is.na>(x),
eval(x):=FALSE]
for (x in c("foo", "bar", "qux")) fbq[is.na
<http://is.na>(eval(x)), eval(x):=FALSE]
for (x in c("foo", "bar", "qux")) fbq[eval(is.na
<http://is.na>(x)), eval(x):=FALSE]
I'm running R 3.0.2 on Linux, data.table 1.8.10.
Thanks in advance,
John
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datatable-help mailing list
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--
Melanie BACOU
International Food Policy Research Institute
Agricultural Economist, HarvestChoice
Work +1(202)862-5699
[email protected]
Visit harvestchoice.org
_______________________________________________
datatable-help mailing list
[email protected]
https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/datatable-help
--
Melanie BACOU
International Food Policy Research Institute
Agricultural Economist, HarvestChoice
Work +1(202)862-5699
E-mail [email protected]
Visit harvestchoice.org
_______________________________________________
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