On Jun 23, 2009, at 7:40 AM, David Hajage wrote:
You can also use if (cond) then {something} if you don't like ifelse()
function. See ?Control.
Had you followed you own advice, you should have seen why this is
completely misleading in the curret context.
"cond
A length-one logical vector that is not NA. Conditions of length
greater than one are accepted with a warning, but only the first
element is used. "
The isn't a FAQ that specifically deals with this conflation, but
there should be.
David
2009/6/23 Peter Flom <peterflomconsult...@mindspring.com>
Dieter Menne wrote:
IF TYPE='TRUCK' and count=12 THEN VEHICLES=TRUCK+((CAR+BIKE)/
2.2);
vehicles <- ifelse(TYPE=='TRUCK' & count=12, TRUCK+((CAR+BIKE)/
2.2),
NA)
Read both versions to an audience, and you will have to admit
that this
is
one of the cases where SAS is superior.
And Peter Dalgaard replied
That's not entirely clear. For instance, SAS is not being clear
about
what happens when the condition is FALSE.
Well, OK, but then it is easy to add an ELSE, and I do find a
structure
such as
IF X = 1 THEN ....
ELSE IF X = 2 THEN ...
ELSE X =
quite a lot easier to both read and write than the equivalent in
R. I also
find the DO loops
in SAS clear.
SAS is also not distinguishing comparison and assignment, but then
again
you don't accidentally do count=12 when you mean count==12....
As a generic matter, SAS (the DATA step) is generally good at things
that are done by sequential sweeps through a data file. The
shortcomings
come in when you do things that can't be done sequentially, or
require
substantial rearranging of data first. x - ave(x,g,median) is an
example
which IIRC requires
proc sort
proc means by group (saving medians to data set)
data step (merge and subtract)
True. But two points:
1) Speaking only for me, but I use an IF THEN ELSE type structure a
lot
more often then I have to do something like the second example.
2) Again, speaking for me, the second sort of thing seems like it
OUGHT to
be hard, while IF THEN seems like it ought to be easy. This may be
because
I learned SAS before R
Peter
Peter L. Flom, PhD
Statistical Consultant
www DOT peterflomconsulting DOT com
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______________________________________________
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David Winsemius, MD
Heritage Laboratories
West Hartford, CT
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