Hi see in line
> -----Original Message----- > From: r-help-boun...@r-project.org [mailto:r-help-bounces@r- > project.org] On Behalf Of Pavneet Arora > Sent: Monday, July 28, 2014 11:08 AM > To: r-help@r-project.org > Subject: [R] Differencing between 2 previous values > > Hello All, > > I am trying to do a simple thing of calculating the absolute difference > between 2 previous values. Since my original data consists of 30 rows, > this column where I am storing my absolute difference values only > consists of 29 rows (called the ?differ?)! And I am having troubling > cbind ing the > 2 columns. Is there any way I can make the first row of ?differ? > column as NA? > > So my data looks like following > dput(data) > tructure(list(week = c(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, > 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30), value > = c(9.45, 7.99, 9.29, 11.66, 12.16, 10.18, 8.04, 11.46, 9.2, 10.34, > 9.03, 11.47, 10.51, 9.4, 10.08, 9.37, 10.62, 10.31, 10, 13, 10.9, 9.33, > 12.29, 11.5, 10.6, 11.08, 10.38, 11.62, 11.31, 10.52)), .Names = > c("week", "value"), row.names = c(NA, -30L), class = "data.frame") > > This is how I calculate my ?diff? column: > differ <- abs(diff(data$value)) differ <- c(NA, abs(diff(data$value))) Regards Petr > Which gives me the following results: > [1] 1.46 1.30 2.37 0.50 1.98 2.14 3.42 2.26 1.14 1.31 2.44 0.96 [13] > 1.11 0.68 0.71 1.25 0.31 0.31 3.00 2.10 1.57 2.96 0.79 0.90 [25] 0.48 > 0.70 1.24 0.31 0.79 > > As you can see this only contains 29 rows, so when I try to cbind it to > my current data, I have an error. > cbind(differ,data) > Error in data.frame(..., check.names = FALSE) : > arguments imply differing number of rows: 29, 30 > > What I ideally want is my new dataset to look as: > Week Value Differ > 1 9.45 NA > 2 7.99 1.46 > 3 9.29 1.30 > > And so on?. > > *********************************************************************** > *********************************************************************** > *********************************************************************** > ** > MORE TH>N is a trading style of Royal & Sun Alliance Insurance plc (No. > 93792). 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