delta(index) is identically 1, so taking first differences is all that
is needed. If the dtatframe's name is df then:
df$dacflong_dx <- c(NA, diff(acflong)) # the slash would not be a
legal character in a variable name unless you jumped through some
hoops that appear entirely without value
If you want to get rid of the first line of df then
df[-1]
--
David Winsemius
On Apr 12, 2009, at 11:55 AM, thaumaturgy wrote:
>
> I am really new to R and ran across a need to take a data matrix and
> calculate an approximation of the first derivative of the data. I
> am more
> than happy to do an "Excel" kind of calculation (deltaY/deltaX)
for
> each
> pair of rows down the matrix, but I don't know how to get R to do
> that kind
> of calculation. I'd like to store it as a 3rd column in the matrix
> as well.
>
> My data looks like this:
> acflong
> 1 1.0000000
> 2 0.9875858
> 3 0.9871751
> 4 0.9867585
> 5 0.9863358
> 6 0.9859070
> 7 0.9854721
> 8 0.9850316
> 9 0.9817161
> 10 0.9812650
>
> and I'd like to generate a table like this:
>
> acflong dacflong/dx
> 1 1.0000000
> 2 0.9875858 -0.01241 #delta(acflong)/delta(index)
> 3 0.9871751 -0.00041
> 4 0.9867585 -0.00042
> 5 0.9863358 -0.00042
> 6 0.9859070 -0.00043
> 7 0.9854721 -0.00043
> 8 0.9850316 -0.00044
> 9 0.9817161 -0.00033
> 10 0.9812650 -0.00045
>
> Is there a way to do this in R and how do I eliminate the first line
> of the
> data?
>
> Thanks,
> -Chris
> --
> View this message in context:
http://www.nabble.com/First-Derivative-of-Data-Matrix-tp23012026p23012026.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
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> PLEASE do read the posting guide
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> and provide commented, minimal, self-contained, reproducible code.
David Winsemius, MD
Heritage Laboratories
West Hartford, CT