Here are a couple of other ways using 'dplyr' and 'data.table' > require(dplyr) > input <- read.table(text = "Year Num + 2001 25 + 2001 75 + 2001 150 + 2002 30 + 2002 85 + 2002 95", header = TRUE) > > input %>% + group_by(Year) %>% + mutate(diff = c(0, diff(Num))) Source: local data frame [6 x 3] Groups: Year [2]
Year Num diff <int> <int> <dbl> 1 2001 25 0 2 2001 75 50 3 2001 150 75 4 2002 30 0 5 2002 85 55 6 2002 95 10 > > # use data.table > require(data.table) Loading required package: data.table data.table 1.9.6 For help type ?data.table or https://github.com/Rdatatable/data.table/wiki The fastest way to learn (by data.table authors): https://www.datacamp.com/courses/data-analysis-the-data-table-way ------------------------------------------------------------------------------------------------------- data.table + dplyr code now lives in dtplyr. Please library(dtplyr)! ------------------------------------------------------------------------------------------------------- Attaching package: ‘data.table’ The following objects are masked from ‘package:dplyr’: between, last > setDT(input) # convert to data.table > input[, diff := c(0, diff(Num)), by = Year][] # print output Year Num diff 1: 2001 25 0 2: 2001 75 50 3: 2001 150 75 4: 2002 30 0 5: 2002 85 55 6: 2002 95 10 > Jim Holtman Data Munger Guru What is the problem that you are trying to solve? Tell me what you want to do, not how you want to do it. On Fri, Oct 28, 2016 at 12:20 AM, Ashta <sewa...@gmail.com> wrote: > Hi all, > > I want to calculate the difference between successive row values to > the first row value within year. > How do I get that? > > Here is the sample of data > Year Num > 2001 25 > 2001 75 > 2001 150 > 2002 30 > 2002 85 > 2002 95 > > Desired output > Year Num diff > 2001 25 0 > 2001 75 50 > 2001 150 125 > 2002 30 0 > 2002 85 55 > 2002 95 65 > > Thank you. > > ______________________________________________ > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > 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. ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see 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.
