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

[Peter Dalgaard BSA]

Paul Johnson <pauljohn at ku.edu> writes:

>      y
> 
> x   1    2     4
>    1 100 66.67  0
>    3  0   0     80
>    4  0   33.33 20
> 
> Pointers appreciated.

prop.table(hmm,2) * 100

> 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

This stuff only works for time series, e.g. cbind(ts(x),lag(ts(x))).
Notice that even then, lag() works in the opposite direction (for
historical reasons).

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907
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