Set a zero at minimum row by group

-----Original Message-----
From: David L Carlson [mailto:dcarlson at tamu.edu]
Sent: Tuesday, December 18, 2012 2:30 PM
To: William Dunlap; 'Carlos Nasher'; r-help at r-project.org
Subject: RE: [R] Set a zero at minimum row by group

This is a bit simpler:

df$x_new <- ave(df$T, df$ID, FUN=function(x)x!=min(x))
df

  ID T x x_new
1  1 1 0     0
2  1 2 1     1
3  1 3 1     1
4  2 1 0     0
5  2 4 1     1
6  3 3 0     0
7  3 5 1     1
8  3 6 1     1
9  3 8 1     1

Are you sure there are no ties for the minimum value?

----------------------------------------------
David L Carlson
Associate Professor of Anthropology
Texas A&M University
College Station, TX 77843-4352

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
project.org] On Behalf Of William Dunlap
Sent: Tuesday, December 18, 2012 10:45 AM
To: Carlos Nasher; r-help at r-project.org
Subject: Re: [R] Set a zero at minimum row by group

You should show what you tried with aggregate and tapply.

You could use ave():

  > wm <- as.logical(ave(df$T, df$ID, FUN=function(x)x==min(x)))
  > df$x_new <- df$x
  > df$x_new[wm] <- 0
  > df

    ID T x x_new
  1  1 1 1     0
  2  1 2 1     1
  3  1 3 1     1
  4  2 1 1     0
  5  2 4 1     1
  6  3 3 1     0
  7  3 5 1     1
  8  3 6 1     1
  9  3 8 1     1

(The as.logical is there because ave() coerces the logical output of
FUN to the type of df$T, numeric, and we need to convert it back to
logical.)

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-

project.org] On Behalf

Of Carlos Nasher
Sent: Tuesday, December 18, 2012 6:10 AM
To: r-help at r-project.org
Subject: [R] Set a zero at minimum row by group

Dear R Helpers,

I'm struggling with a data preparation problem. I feel that it is a

quite

easy task but I don't get it done. I hope you can help me with that.

I have a data frame looking like this:

ID <- c(1,1,1,2,2,3,3,3,3)
T <- c(1,2,3,1,4,3,5,6,8)
x <- rep(1,9)
df <- data.frame(ID,T,x)

df

ID T x
1 1 1
1 2 1
1 3 1
2 1 1
2 4 1
3 3 1
3 5 1
3 6 1
3 8 1

I want to manipulate the x column in a way that for each customer

(ID) at

the minimum of T the x value is set to zero. The result should look

like

this:

ID T x x_new
1 1 1     0
1 2 1     1
1 3 1     1
2 1 1     0
2 4 1     1
3 3 1     0
3 5 1     1
3 6 1     1
3 8 1     1

I already tried the aggregate() and apply() function, but I don't get

the

result I'm looking for. I would glad if you could help me out.

Best regards,
Carlos

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