# [R] Calculating column differences

Jeff Reichman re|chm@nj @end|ng |rom @bcg|ob@|@net
Wed Mar 24 19:21:08 CET 2021

```Gerrit

Changed my approach 😊

df <- data.frame(ID=1:5,Score=4*2:6)

df %>%

mutate(score_diff = Score - lag(Score, default = 0))

Jeff

-----Original Message-----
From: R-help <r-help-bounces using r-project.org> On Behalf Of Gerrit Eichner
Sent: Wednesday, March 24, 2021 11:53 AM
To: r-help using r-project.org
Subject: Re: [R] Calculating column differences

Dear Jeff,

read diff's help page, and you'll find out what is wrong with your expectation.

What do think diff(df\$Score) should give for the first element in df\$Score??

Hth  --  Gerrit

---------------------------------------------------------------------

Dr. Gerrit Eichner                   Mathematical Institute, Room 212

<mailto:gerrit.eichner using math.uni-giessen.de> gerrit.eichner using math.uni-giessen.de   Justus-Liebig-University Giessen

Tel: +49-(0)641-99-32104          Arndtstr. 2, 35392 Giessen, Germany

<http://www.uni-giessen.de/eichner> http://www.uni-giessen.de/eichner

---------------------------------------------------------------------

Am 24.03.2021 um 17:48 schrieb Jeff Reichman:

> r-help forum

>

>

>

> I'm trying to calculate the diff between two rows and them mutate the

> difference into a new column. I'm using the diff function but not

> giving me what I want.

>

>

>

> df <- data.frame(ID=1:5,Score=4*2:6)

>

>

>

> What a want  where

>

>    ID Score  diff

>

> 1  1     8      8

>

> 2  2    12     4

>

> 3  3    16     4

>

> 4  4    20     4

>

> 5  5    24     4

>

>

>

> What I am getting

>

>    ID Score  diff

>

> 1  1     8      NA

>

> 2  2    12     4

>

> 3  3    16     4

>

> 4  4    20     4

>

> 5  5    24     4

>

>

>

> Jeff

>

>

>

>

>             [[alternative HTML version deleted]]

>

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> and provide commented, minimal, self-contained, reproducible code.

>

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