Calculating column differences

df <- data.frame(ID=1:5,Score=4*2:6)
df1 <- rbind(c(0,0), df)
cbind(df1, "diff"=c(NA, diff(df1$Score)) )

Dear Jeff,

Rather than diff-ing a linear vector you're trying to diff values from 
two different rows. Also you indicate that you want to place the 
diff-ed value in the 'lower' row of a new column. Try this (note 
insertion of an initial "zero" row):

df <- data.frame(ID=1:5,Score=4*2:6)
df1 <- rbind(c(0,0), df)
cbind(df1, "diff"=c(0, diff(df1$Score)) )

  ID Score diff
1  0     0    0
2  1     8    8
3  2    12    4
4  3    16    4
5  4    20    4
6  5    24    4

HTH, Bill.

W. Michels, Ph.D.



On Wed, Mar 24, 2021 at 9:49 AM Jeff Reichman <reichmanj at sbcglobal.net> wrote:

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




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