# [R] Add a column to a data frame with value based on the percentile of the row

arun smartpink111 at yahoo.com
Wed Jul 31 14:56:35 CEST 2013

```Hi,

set.seed(24)
dat1<- data.frame(ID=1:500,value=rnorm(500))
dat1 <- dat1[order(-dat1\$value),]
row.names(dat1)<-1:nrow(dat1) ########

indx<-round(quantile(as.numeric(row.names(dat1)),probs=c(0.05,0.20,0.50,1)))
indx1<-findInterval(row.names(dat1),indx,rightmost.closed=TRUE)
dat1\$SEGMENT<- as.character(factor(indx1,labels=c("Top 5%","5 to 20","20 to 50", "Bottom 50")))

A.K.

Hi Arun Kirshna,

I have tested your method and it will work for me.
I only run into one problem. Before I want to do this operation I have sorted my data frame so my rownumbers ar not subsequent.

You can see if you first order your example data frame like:
dat1 <- dat1[order(-dat1\$value),]

ID    value   SEGMENT
237 237 3.538552  20 to 50
21   21 3.376149    Top 5%
421 421 3.015634 Bottom 50
339 339 2.855991 Bottom 50
119 119 2.589574  20 to 50
12   12 2.512276    Top 5%

Do you have a solution for this?

----- Original Message -----
From: arun <smartpink111 at yahoo.com>
To: Dark <info at software-solutions.nl>
Cc: R help <r-help at r-project.org>
Sent: Wednesday, July 31, 2013 7:48 AM
Subject: Re: [R] Add a column to a data frame with value based on the percentile of the row

Hi,
May be this helps:
set.seed(24)
dat1<- data.frame(ID=1:500,value=rnorm(500))
indx<-round(quantile(as.numeric(row.names(dat1)),probs=c(0.05,0.20,0.50,1)))
indx1<-findInterval(row.names(dat1),indx,rightmost.closed=TRUE)
dat1\$SEGMENT<- as.character(factor(indx1,labels=c("Top 5%","5 to 20","20 to 50", "Bottom 50")))
#  ID      value SEGMENT
#1  3 -0.7859574  Top 5%
#2  3  1.0117428  Top 5%
#3  8 -2.1558035  Top 5%
#4  6  1.7803880  Top 5%
#5  7  0.4192816  Top 5%
#6 10 -1.0142512  Top 5%
tail(dat1)
#    ID      value   SEGMENT
#495  1  0.3571848 Bottom 50
#496  9 -1.1971854 Bottom 50
#497  5  0.3544896 Bottom 50
#498  8 -0.1562356 Bottom 50
#499  8 -0.2994321 Bottom 50
#500  8 -0.4170319 Bottom 50

A.K.

----- Original Message -----
From: Dark <info at software-solutions.nl>
To: r-help at r-project.org
Cc:
Sent: Wednesday, July 31, 2013 5:37 AM
Subject: [R] Add a column to a data frame with value based on the percentile of the row

Hi all,

I think this should be an easy question for the guru's out here.

I have this large data frame (2.500.000 rows, 15 columns) and I want to add
a column named "SEGMENT" to it.
The first 5% rows (first 125.000 rows) should have the value "Top 5%" in the
SEGMENT column
Then the rows from 5% to 20% should have the value "5 to 20"
Then 20-50% should have the value "20 to 50"
And the last 50% of the rows should have the value "Bottom 50"

What is the easiest way of doing this? I was thinking of using quantile but
then I should have some rownumber column.

Regards Derk

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