Thank you for that simple answer. Really appreciate it.



From:   PIKAL Petr <petr.pikal@precheza.cz>
To:     Pavneet Arora/UK/RoyalSun@RoyalSun, "r-help@r-project.org" 
<r-help@r-project.org>
Date:   28/07/2014 10:26
Subject:        RE: [R] Differencing between 2 previous values



Hi

see in line

> -----Original Message-----
> From: r-help-bounces@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?.
>
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> 93792). Registered in England and Wales at St. Markâ??s Court, Chart
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>
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MORE TH>N is a trading style of Royal & Sun Alliance Insurance plc (No. 93792). Registered in England and Wales at St. Mark’s Court, Chart Way, Horsham, West Sussex, RH12 1XL. 

Authorised by the Prudential Regulation Authority and regulated by the Financial Conduct Authority and the Prudential Regulation Authority.
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