[R] regression on data subsets in datafile

[Gabor Grothendieck]

On Mon, Sep 12, 2011 at 3:42 AM, marcel <marcelcurlin at gmail.com> wrote:
> I have data of the form
>
> tC <- textConnection("
> Subject Date    parameter1
> bob     3/2/99  10
> bob     4/2/99  10
> bob     5/5/99  10
> bob     6/27/99 NA
> bob     8/35/01 10
> bob     3/2/02  10
> steve   1/2/99  4
> steve   2/2/00  7
> steve   3/2/01  10
> steve   4/2/02  NA
> steve   5/2/03  16
> kevin   6/5/04  24
> ")
> data <- read.table(header=TRUE, tC)
> close.connection(tC)
> rm(tC)
>
> I am trying to calculate rate of change of parameter1 in units/day for each
> person. I think I need something like:

Try this:

data$Date <- as.Date(data$Date, "%m/%d/%y")
fm <- lm(parameter1 ~ Subject / Date - 1, data)
coef(fm)


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