[R] Suprising R behaviour

[Ilgaz S]

Thank you all for answering such a newbie question. :) David thank you for
your example too.
Best wishes, I.S
On Nov 14, 2015 18:28, "David L Carlson" <dcarlson at tamu.edu> wrote:

> My original answer works fine as long as fin_hyp contains only one
> definition for the line, but if it contains more than one, R will use a
> different line for each test which is probably not what you want (e.g. the
> first point will be tested against the first line and the second point
> against the second line, etc). In that case a loop or apply function would
> be needed:
>
> > data <- data.frame(x = c(1,2,3,1,1,1), y = c(1,2,3,4,6,7))
> > fin_hyp <- data.frame(slope = c(2, 1, -2), constant = c(1, -1, 7))
> > outputs <- apply(fin_hyp, 1, function(z) data$y > z[1] * data$x  + z[2])
> > outputs
>       [,1] [,2]  [,3]
> [1,] FALSE TRUE FALSE
> [2,] FALSE TRUE FALSE
> [3,] FALSE TRUE  TRUE
> [4,]  TRUE TRUE FALSE
> [5,]  TRUE TRUE  TRUE
> [6,]  TRUE TRUE  TRUE
>
> The first column is the result for the first equation (row in fin_hyp) and
> so on.
>
> David L. Carlson
> Department of Anthropology
> Texas A&M University
>
>
> -----Original Message-----
> From: David L Carlson
> Sent: Saturday, November 14, 2015 9:57 AM
> To: 'Duncan Murdoch' <murdoch.duncan at gmail.com>; Ilgaz S <
> ilgaz.somer at gmail.com>; r-help at r-project.org
> Subject: RE: [R] Suprising R behaviour
>
> You definitely need to learn about the differences between R and the other
> languages that you are familiar with. You've done some work since you
> mention the apply() family, but those are just another way of programming a
> loop. In many cases (including this one), a loop is not needed. Here's your
> code in a plain text message with some additions:
>
> data <- data.frame(x = c(1,2,3,1,1,1), y = c(1,2,3,4,6,7))
> # fin_hyp could just as easily be a data frame or a matrix
> fin_hyp <- list(slope = 2, constant = 1)
> # R vectorizes the following command and automatically computes the
> # result for each row in "data"
> outputs <- data['y'] > fin_hyp['slope'] * data['x']  + fin_hyp['constant']
> outputs
> # Add a plot showing points above and below the line
> # ifelse is vectorized so it creates a vector with
> # 16 (symbol for solid circle) if above the line and
> # 1 (open circle) if below the line
> sym <- ifelse(outputs, 16, 1)
> plot(y~x, data, pch=sym)
> abline(a=fin_hyp$constant, b=fin_hyp$slope)
>
>
> David L. Carlson
> Department of Anthropology
> Texas A&M University
>
> -----Original Message-----
> From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of Duncan
> Murdoch
> Sent: Friday, November 13, 2015 1:16 PM
> To: Ilgaz S <ilgaz.somer at gmail.com>; r-help at r-project.org
> Subject: Re: [R] Suprising R behaviour
>
> On 13/11/2015 8:11 AM, Ilgaz S wrote:
> > Hello everybody, I am new to R and I discovered something that suprise me
> > and I have a question about it.
> > Today I wanted to return a bit array which represents this:
> >
> > if( arbitrary point above the line)
> >       return TRUE
> > else
> >       return FALSE
> >
> > First I tought I would use for loop and access every element of the data.
> > Then I tend to use lapply function.
> >
> > At the end, I accidently done that without using any if/else statement. (
> > or for loop )  Here is the code:
>
> I can't read your code (you posted in HTML, don't do that), but it
> sounds as though you have discovered vectorized operations.  These are
> central to good R programming, and are well described in the
> Introduction to R manual.
>
> Duncan Murdoch
> >
> > data <- data.frame(x= c(1,2,3,1,1,1), y = c(1,2,3,4,6,7))fin_hyp <-
> > list(slope=2,constant=1)outputs <- data['y'] > fin_hyp['slope'] *
> > data['x']  +fin_hyp['constant']outputs
> >
> > What is R doing here? It is using loop somewhere inside? Is this code
> > more efficient than other methods I mentioned?
> >
> > Thank you, I.S.
> >
> >       [[alternative HTML version deleted]]
> >
> > ______________________________________________
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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.
>
> ______________________________________________
> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

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