On Jun 9, 2012, at 1:02 PM, Onur Uncu wrote:
Thank you Michael. One follow up question: In the solution using
apply(), why are we feeding x[2] inside testfun instead of x[[2]]?
Aren't we supposed to feed the vector of values to the function, which
is achieved by x[[2]]?
`apply` sends the columns of data to the receiving function as a
vector. It has already effectively done an unlist operation on
dfrm[ row, ]. If I am reading the code for `apply` correctly that is
because it coerced its dataframe argument to a matrix with this code:
if (is.object(X))
X <- if (dl == 2L)
as.matrix(X)
else as.array(X)
--
David.
Thnks.
On Sat, Jun 9, 2012 at 3:38 PM, R. Michael Weylandt
<michael.weyla...@gmail.com> wrote:
No worries -- it's an important question and it introduces you to one
of the most important R idioms. [And you get bonus points for
having a
well formed question!]
You're probably looking for something like this:
apply(testframe, 1, function(x) testfun(x[2]))
Which goes row-by-row and substitutes the second element (your col2)
into testfun leaving the y= unsupplied and hence defaulting to 2.
This
seems a little kludgy, however, in light of the below. (Also, if you
have a data frame of multiple types, it seems to get in trouble
quicker than I would have imagined)
Note that this is not particularly efficient and you could just use
testfun(testframe[["col2"]])
instead using the magic of vectorization. Very rarely do you need to
do things "one-by-one" except for recursive/state-dependent
simulations.
Best,
Michael
On Sat, Jun 9, 2012 at 9:12 AM, Onur Uncu <onuru...@gmail.com> wrote:
Apologees the novice question. Currently climbing up the learning
curve of R.
Suppose I have the following function and the data.frame:
testfun<-function(x=1,y=2) x+y
testframe=data.frame(col1=c(1,2),col2=c(3,4))
When evaluating testfun, I want to use the default value for y
(which
is 2) and for x, I want to feed (one by one) the values in col2 of
testframe. How can I achieve this please? Not having much success
with
apply()
Thanks for any help.
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______________________________________________
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
David Winsemius, MD
West Hartford, CT
______________________________________________
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
