[R] group data based on row value

[Ye Lin]

hey, I want to divide my data into three groups based on the value in one
column with group name.

dat:

Var
0
0.2
0.5
1
4
6

I tried:

dat <- cbind(dat, group=cut(dat$Var, breaks=c(0.1,0.6)))

But it doesnt work, I want to group those <0.1 as group A, 0.1-0.6 as group
B, >0.6 as group C

Thanks for your help!

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[arun]

Hi,
Try:
dat<- read.table(text="

Var
0
0.2
0.5
1
4
6

",sep="",header=TRUE)

res1<-within(dat,group<-factor(findInterval(Var,c(-Inf,0.1,0.6),rightmost.closed=TRUE),labels=LETTERS[1:3]))
 res1
 # Var group
#1 0.0     A
#2 0.2     B
#3 0.5     B
#4 1.0     C
#5 4.0     C
#6 6.0     C

#or

res2<-within(dat,group<-factor(cut(Var,breaks=c(-Inf,0.1,0.6,Inf)),labels=LETTERS[1:3]))
 identical(res1,res2)
#[1] TRUE
A.K.

>hey, I want to divide my data into three groups based on the value in one
>column with group name.
>
>dat:
>
>Var
>0
>0.2
>0.5
>1
>4
>6
>
>I tried:
>
>dat <- cbind(dat, group=cut(dat$Var, breaks=c(0.1,0.6)))
>
>But it doesnt work, I want to group those <0.1 as group A, 0.1-0.6 as group
>B, >0.6 as group C
>
>Thanks for your help!

[Jeff Newmiller]

dat$group <- cut( dat$Var, breaks=c(-Inf,0.1, 0.6,Inf))
levels(dat$group) <- LETTERS[1:3]

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[David Carlson]

The OP indicated that the middle group should be closed on both ends, i.e.
[0.1, 0.6].

> dat2 <- rbind(dat, 0.1, 0.6)
> dat2$group <- factor(ifelse(dat2$Var<.1, "A", ifelse(dat2$Var>.6, "C",
"B")))
> dat2
Var group
1 0.0 A
2 0.2 B
3 0.5 B
4 1.0 C
5 4.0 C
6 6.0 C
7 0.1 B
8 0.6 B

Does it but would be clumsy for more than three groups. Depending on the
precision of the numbers something like

> dat2$group <- cut( dat2$Var, breaks=c(-Inf, 0.1-.0001, 0.6+.0001, Inf),
labels=LETTERS[1:3])
> dat2
Var group
1 0.0 A
2 0.2 B
3 0.5 B
4 1.0 C
5 4.0 C
6 6.0 C
7 0.1 B
8 0.6 B

would also work.

-------------------------------------
David L Carlson
Associate Professor of Anthropology
Texas A&M University
College Station, TX 77840-4352