[R] function that calculates using preceding records

[Seth Bigelow]

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


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