Aha, this solution is even more elegant than that of the previous suggestion.
Thanks for alerting me to the capabilities of plyr!
--Seth
-----Original Message-----
From: Dennis Murphy [mailto:djmuser at gmail.com]
Sent: Tuesday, February 10, 2015 2:14 PM
To: Seth Bigelow
Subject: Re: [R] function that calculates using preceding records
Hi:
Here's another way. If I understand this correctly, you can get the
diameters by setting the NA values in d to zero, taking the cumulative sum of d
(within treecode) and then subtracting the result from diam[1]. Since I'm
used to doing this type of thing in data manipulation packages, I prefer to
write a function to do the work and then run it in concert with plyr::ddply().
Letting DF represent the name of your data frame,
# Function to apply to each subgroup (treecode ID) f <- function(d)
{
d <- d[order(-d$year), ] # order by decreasing year
d$rw[is.na(d$rw)] <- 0 # set NAs in rw to 0
d$diam <- d$d[1] - cumsum(d$rw) # compute past diams
d # return modified data frame
}
library(plyr)
# This applies the function f to each sub-data frame defined # by unique values
of treecode ddply(DF, .(treecode), f)
treecode year rw d diam
1 TC146 2014 0.000 60.0 60.000
2 TC146 2013 1.750 NA 58.250
3 TC146 2012 1.810 NA 56.440
4 TC146 2011 1.390 NA 55.050
5 TC146 2010 1.940 NA 53.110
6 TC147 2014 0.000 55.5 55.500
7 TC147 2013 1.260 NA 54.240
8 TC147 2012 1.115 NA 53.125
9 TC147 2011 1.025 NA 52.100
10 TC147 2010 1.495 NA 50.605
11 TC148 2014 0.000 34.0 34.000
12 TC148 2013 0.300 NA 33.700
13 TC148 2012 0.335 NA 33.365
14 TC148 2011 0.315 NA 33.050
15 TC148 2010 0.455 NA 32.595
16 TC149 2014 0.000 8.0 8.000
17 TC149 2013 0.080 NA 7.920
18 TC149 2012 0.125 NA 7.795
19 TC149 2011 0.120 NA 7.675
20 TC149 2010 0.125 NA 7.550
HTH,
Dennis
On Tue, Feb 10, 2015 at 6:30 AM, Seth Bigelow <seth at forestadapt.org>
wrote:> Greetings:
>
>
>
> My dataframe has 4 variables: treecode, year, rw (tree ring width),
> and d (tree diameter). The d variable
>
> only has data for 2014. I wish to calculate earlier diameters by
> subtracting each year's growth (rw) from the
>
> previous year's diameter, by treecode. Can anyone help me with a
> function or statement that will do this?
>
> Sample dataset below: In this example, d in year 2013 for treecode
> TC149 would be 7.92 = 8.0 - 0.080.
>
>
>
> "treecode","year","rw","d"
>
> "1","TC149",2014,NA,8
>
> "2","TC149",2013,0.08,NA
>
> "3","TC149",2012,0.125,NA
>
> "4","TC149",2011,0.12,NA
>
> "5","TC149",2010,0.125,NA
>
> "6","TC148",2014,NA,34
>
> "7","TC148",2013,0.3,NA
>
> "8","TC148",2012,0.335,NA
>
> "9","TC148",2011,0.315,NA
>
> "10","TC148",2010,0.455,NA
>
> "11","TC147",2014,NA,55.5
>
> "12","TC147",2013,1.26,NA
>
> "13","TC147",2012,1.115,NA
>
> "14","TC147",2011,1.025,NA
>
> "15","TC147",2010,1.495,NA
>
> "16","TC146",2014,NA,60
>
> "17","TC146",2013,1.75,NA
>
> "18","TC146",2012,1.81,NA
>
> "19","TC146",2011,1.39,NA
>
> "20","TC146",2010,1.94,NA
>
>
>
>
>
> Seth W. Bigelow
>
>
> [[alternative HTML version deleted]]
>
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