[R] A couple of little R things I can't figure out (column percents,regression with lagged variables)

[Joerg Maeder]

hallo paul,

for the percentages use this code (the trick is to use transpose twice)

t(t(hm)/apply(hmm,2,sum))*100




Paul Johnson wrote:
> 
> Simple usage questions that I ought to be able to figure on my own, but
> can't.
> 
> 1.I'm able to produce a cross tabulation table showing counts with
> either table or xtabs.  But I want column percentages for
> interpretation, and it seems stupid to sit there with a calculator
> figuring marginals and column percentages.  How to make R do it after this:
> 
>  > x <- c(1,3,1,3,1,3,1,3,4,4)
>  > y <- c(2,4,1,4,2,4,1,4,2,4)
>  > hmm <- table(x,y)
>  > hmm
>     y
> x   1 2 4
>    1 2 2 0
>    3 0 0 4
>    4 0 1 1
> 
> #I can get the column sums:
>  > tots <- apply(hmm,2,sum)
> 
> and I can get the total N of counts, but don't understand how to make it
> calculate column percents, as in
> 
>      y
> 
> x   1    2     4
>    1 100 66.67  0
>    3  0   0     80
>    4  0   33.33 20
> 
> Pointers appreciated.
> 
> 2. A student said here's  y, a vector representing a time series, and
> here's x, a vector representing a time series. I want to do a
> conventional regression of y on the lag of x. In sas you do xlag=lag(x)
> and then use xlag in a regresson.  I just want something simple like
> lm(y~lag(x)). But in R base there's no lag.
> 
> So I can get it the old fashioned way:
>  > xx <- c(NA,x)
>  > modl <- lm(y~xx[1:length(y)])
>  > summary(modl)
> 
> One sidenote is that summary does not include any mention of the fact
> that 1 observation was lost due to missing value. That seems bad to me.
> 
> I see the lag function in ts, but when I use it, it doesn't change x, so
> obviously I don't see the point of that.
> 
>  > z <- lag (x)
>  > z
>   [1] 1 3 1 3 1 3 1 3 4 4
> 
> So long, thanks in advance, greetings, etc...
> 
> --
> Paul E. Johnson                       email: pauljohn at ukans.edu
> Dept. of Political Science            http://lark.cc.ku.edu/~pauljohn
> University of Kansas                  Office: (785) 864-9086
> Lawrence, Kansas 66045                FAX: (785) 864-5700
> 
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-- 
Joerg Maeder    .:|:||:..:.||.::   maeder at atmos.umnw.ethz.ch
Tel: +41 1 633 36 25   .:|:||:..:.||.::   
http://www.iac.ethz.ch/staff/maeder
PhD student at INSTITUTE FOR ATMOSPHERIC AND CLIMATE SCIENCE (IACETH)
ETH ZÜRICH Switzerland
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