[R] How to index the occasions in a vector repeatedly under condition 1? if not, it will give a new index.

[Rui Barradas]

Hello,

First of all, a note about your reproducible example.

When you write diff <- x - lag(x) there are two things to be said.

1. There is a base R function named 'diff', it is better to use another 
name.

diff(x)
#[1]   0   0   0   8   0 577  69   0

2. There are also several functions named 'lag', one of them in base 
package stats.

x - lag(x)
#[1] 0 0 0 0 0 0 0 0 0
#attr(,"tsp")
#[1] 0 8 1

This is not the one you are using.

x - dplyr::lag(x)
#[1]  NA   0   0   0   8   0 577  69   0

That's the one. When you have a package loaded in your session, please 
start your scripts with library(<pkgname>), in this case library(dplyr).


Now for the question's problem. I will use a different name, 'd', not 
'diff'. And qualify the function name with the package name prefix.

The main problem is the NA in the first element of 'd', without it 
cumsum(d > 15) would be enough. This works because the logical values 
FALSE/TRUE are coded as 0/1 and their cumulative sum goes up every time 
a TRUE is found.

d <- x - dplyr::lag(x)
cumsum(is.na(d) | d > 15)
#[1] 1 1 1 1 1 1 2 3 3


Hope this helps,

Rui Barradas


Às 06:56 de 19/02/20, Lijun Zhao escreveu:
> Dear All,
> 
> could you please help me how to get the output from the following example?
> 
> 
> x<-c(543,  543,  543,  543,  551 , 551 ,1128 ,1197, 1197)
> 
> diff<-x-lag(x)
> 
> diff
> 
> [1]  NA   0   0   0   8   0 577  69   0
> 
> how to index the occassions in x repeatedly if the diff>15? if not, it will
> give a new index
> 
> i want the output be like y
> 
> y<-c(1,1,1,1,1,1,2,3,3)
> 
> 
> thanks,
> 
> 
> Lijun
> 
> 	[[alternative HTML version deleted]]
> 
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