numbering observations: help please!

Dear Friends,

I have the very simple problem of needing to number observations in a data
frame. After scratching the rest of my hair off my head without inspiration,
I'm using a silly loop. I'm sure that there is a much more elegant and
faster solution - can anyone help?

Here is an example:

my.data <- data.frame (person=c(1,1,1,1,2,2,3,3,3,3,3,3,3,4,4,4))   # now I
want to number those observations sequentially
# for each person

my.data$item.number <- 0
for (i in 1:length(unique(my.data$person))) {
	my.data$item.number [which (my.data$person == unique(my.data$person)[i])]
<- seq (1:dim(tmp)[1]) }

my.data$item.number <- 
with(my.data,unlist(tapply(1:length(person),person,function(x){1:length(x)})))

     cheers,

         Rolf Turner

Dear Friends,

I have the very simple problem of needing to number observations in a data
frame. After scratching the rest of my hair off my head without inspiration,
I'm using a silly loop. I'm sure that there is a much more elegant and
faster solution - can anyone help?

Here is an example:

my.data <- data.frame (person=c(1,1,1,1,2,2,3,3,3,3,3,3,3,4,4,4))   # now I
want to number those observations sequentially
# for each person

my.data$item.number <- 0
for (i in 1:length(unique(my.data$person))) {
	my.data$item.number [which (my.data$person == unique(my.data$person)[i])]
<- seq (1:dim(tmp)[1]) }

Dunno what "tmp" is... but try this:

my.data$item.number <- 1
my.data$item.number <- ave( my.data$item.number, my.data$person, 
FUN=cumsum )

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HI, 
Try this: 
my.data$item_Num<- ave(my.data[,1],my.data[,1],FUN=seq_along) 

head(my.data) 
# ?person item_Num 
#1 ? ? ?1 ? ? ? ?1 
#2 ? ? ?1 ? ? ? ?2 
#3 ? ? ?1 ? ? ? ?3 
#4 ? ? ?1 ? ? ? ?4 
#5 ? ? ?2 ? ? ? ?1 
#6 ? ? ?2 ? ? ? ?2 

#or, 
unlist(tapply(my.data[,1],my.data[,1],FUN=seq_along),use.names=FALSE) 
# [1] 1 2 3 4 1 2 1 2 3 4 5 6 7 1 2 3
#or
?unlist(sapply(split(my.data,my.data[,1]),function(x) 1:nrow(x)),use.names=FALSE)
# [1] 1 2 3 4 1 2 1 2 3 4 5 6 7 1 2 3

A.K.


----- Original Message -----
From: Paul Artes <paul_h_artes at yahoo.co.uk>
To: r-help at r-project.org
Cc: 
Sent: Tuesday, November 13, 2012 8:50 PM
Subject: [R] numbering observations: help please!

Dear Friends,

I have the very simple problem of needing to number observations in a data
frame. After scratching the rest of my hair off my head without inspiration,
I'm using a silly loop. I'm sure that there is a much more elegant and
faster solution - can anyone help? 

Here is an example:

my.data <- data.frame (person=c(1,1,1,1,2,2,3,3,3,3,3,3,3,4,4,4))?  # now I
want to number those observations sequentially 
# for each person

my.data$item.number <- 0
for (i in 1:length(unique(my.data$person))) {
??? my.data$item.number [which (my.data$person == unique(my.data$person)[i])]
<- seq (1:dim(tmp)[1]) }






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