[R] First Derivative of Data Matrix
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 1.000 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 1.000 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. __ R-help@r-project.org mailing list 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.
Re: [R] First Derivative of Data Matrix
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 1.000 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 1.000 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. __ R-help@r-project.org mailing list 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. David Winsemius, MD Heritage Laboratories West Hartford, CT __ R-help@r-project.org mailing list 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.
Re: [R] First Derivative of Data Matrix
However, estimating derivatives from differencing data amplifies minor errors. Less noisy estimates can be obtained by first smoothing and then differentiating the smooth. The fda package provides substantial facilities for this. Hope this helps. Spencer Graves David Winsemius wrote: 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] __ R-help@r-project.org mailing list 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.
Re: [R] First Derivative of Data Matrix
David, Thank you! -Chris -- View this message in context: http://www.nabble.com/First-Derivative-of-Data-Matrix-tp23012026p23015941.html Sent from the R help mailing list archive at Nabble.com. __ R-help@r-project.org mailing list 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.
