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<div class="moz-cite-prefix"><br>
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.<br>
<br>
Matt<br>
<br>
On 12/02/14 17:58, John Laing wrote:<br>
</div>
<blockquote
cite="mid:CAA3Wa=u2PwRW_Od4XTodtZ4uDSN7RZmOs33Uaaix8GN7OuRpag@mail.gmail.com"
type="cite">
<div dir="ltr">Thanks, Matt! With a slight amendment that works
great:
<div>
<div>for (x in c("foo", "bar", "qux")) set(fbq, which(<a
moz-do-not-send="true" href="http://is.na">is.na</a>(fbq[[x]])),
x, FALSE)</div>
</div>
<div><br>
</div>
<div>Which highlights an opportunity to say that I really
appreciate the unusually helpful error messages in this
package.</div>
<div><br>
</div>
<div>-John</div>
</div>
<div class="gmail_extra"><br>
<br>
<div class="gmail_quote"> On Wed, Feb 12, 2014 at 12:44 PM, Matt
Dowle <span dir="ltr"><<a moz-do-not-send="true"
href="mailto:mdowle@mdowle.plus.com" target="_blank">mdowle@mdowle.plus.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000">
<div><br>
Hi John,<br>
<br>
In examples like this I'd use set() and [[, since it's
a bit easier to write but memory efficient too.<br>
<br>
for (x in c("foo", "bar", "qux")) set(fbq, <a
moz-do-not-send="true" href="http://is.na"
target="_blank">is.na</a>(fbq[[x]]), x,
FALSE) [untested]<br>
<br>
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.<br>
<br>
Or, use get() in either i or j rather than eval().<br>
<br>
HTH, Matt
<div>
<div class="h5"><br>
<br>
<br>
On 12/02/14 17:24, John Laing wrote:<br>
</div>
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<blockquote type="cite">
<div>
<div class="h5">
<div dir="ltr">Let's say I merge together several
data.tables such that I wind up<br>
with lots of NAs:<br>
<br>
require(data.table)<br>
foo <- data.table(k=1:4, foo=TRUE, key="k")<br>
bar <- data.table(k=3:6, bar=TRUE, key="k")<br>
qux <- data.table(k=5:8, qux=TRUE, key="k")<br>
fbq <- merge(merge(foo, bar, all=TRUE), qux,
all=TRUE)<br>
print(fbq)<br>
# k foo bar qux<br>
# 1: 1 TRUE NA NA<br>
# 2: 2 TRUE NA NA<br>
# 3: 3 TRUE TRUE NA<br>
# 4: 4 TRUE TRUE NA<br>
# 5: 5 NA TRUE TRUE<br>
# 6: 6 NA TRUE TRUE<br>
# 7: 7 NA NA TRUE<br>
# 8: 8 NA NA TRUE<br>
<br>
I want to go through those columns and turn each
NA into FALSE. I can<br>
do this by writing code for each column:<br>
<br>
fbq.cp <- copy(fbq)<br>
fbq.cp[<a moz-do-not-send="true"
href="http://is.na" target="_blank">is.na</a>(foo),
foo:=FALSE]<br>
fbq.cp[<a moz-do-not-send="true"
href="http://is.na" target="_blank">is.na</a>(bar),
bar:=FALSE]<br>
fbq.cp[<a moz-do-not-send="true"
href="http://is.na" target="_blank">is.na</a>(qux),
qux:=FALSE]<br>
print(fbq.cp)<br>
# k foo bar qux<br>
# 1: 1 TRUE FALSE FALSE<br>
# 2: 2 TRUE FALSE FALSE<br>
# 3: 3 TRUE TRUE FALSE<br>
# 4: 4 TRUE TRUE FALSE<br>
# 5: 5 FALSE TRUE TRUE<br>
# 6: 6 FALSE TRUE TRUE<br>
# 7: 7 FALSE FALSE TRUE<br>
# 8: 8 FALSE FALSE TRUE<br>
<br>
But I can't figure out how to do it in a loop.
More precisely, I can't<br>
figure out how to make the [ operator evaluate its
first argument in<br>
the context of the data.table. All of these have
no effect:<br>
for (x in c("foo", "bar", "qux")) fbq[<a
moz-do-not-send="true" href="http://is.na"
target="_blank">is.na</a>(x), eval(x):=FALSE]<br>
for (x in c("foo", "bar", "qux")) fbq[<a
moz-do-not-send="true" href="http://is.na"
target="_blank">is.na</a>(eval(x)),
eval(x):=FALSE]<br>
for (x in c("foo", "bar", "qux")) fbq[eval(<a
moz-do-not-send="true" href="http://is.na"
target="_blank">is.na</a>(x)), eval(x):=FALSE]<br>
<br>
I'm running R 3.0.2 on Linux, data.table 1.8.10.<br>
<br>
Thanks in advance,<br>
John</div>
<br>
<fieldset></fieldset>
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