[R] Collapsing a vector/data-frame based on the previous values

[arun]

Hello,

Try this:

#dat1 - data
 diff2<-c(TRUE,ifelse(diff(dat1$State)>0|diff(dat1$State)<0,TRUE,FALSE))
  dat1[diff2,1:2]
 #        Date State
#1  24/07/2012     1
#6  24/07/2012    -1
#9  27/07/2012     1
#10 28/07/2012    -1


A.K.



----- Original Message -----
From: Raghuraman Ramachandran <optionsraghu at gmail.com>
To: R Project Help <r-help at r-project.org>
Cc: 
Sent: Tuesday, July 24, 2012 2:40 AM
Subject: [R] Collapsing a vector/data-frame based on the previous values

Hello

I have a data frame like this:
dput(states)
structure(list(Date = c("24/07/2012", "25/07/2012", "26/07/2012",
"27/07/2012", "28/07/2012", "24/07/2012", "25/07/2012", "26/07/2012",
"27/07/2012", "28/07/2012"), State = c(1L, 1L, 1L, 1L, 1L, -1L,
-1L, -1L, 1L, -1L)), .Names = c("Date", "State"), class = "data.frame",
row.names = c(NA,
-10L))

> State

      Date State
1  24/07/2012     1
2  25/07/2012     1
3  26/07/2012     1
4  27/07/2012     1
5  28/07/2012     1
6  24/07/2012    -1
7  25/07/2012    -1
8  26/07/2012    -1
9  27/07/2012     1
10 28/07/2012    -1

I wish to collapse it into a smaller one based on the state value. If state
is 1 already then the second state (and the row) is to be removed till a
new state is found and so on.. States can be 1 or -1 only. So in the
previous example the new data frame should be:

  Date State  24/07/2012 1  24/07/2012 -1  27/07/2012 1  28/07/2012 -1  Can
someone help?

Thx
Raghu

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