[R] counting run lengths

[Mario Lavezzi]

Hi Dimitris, thank you very much.
Actually, I have not  specified the following:  i want to consider only
the "most recent" sequence of zeros, that is the last part of the time
series.

That is, If  I have:

    [,1] [,2] [,3] [,4]
[1,]    0    1    0    1
[2,]    1    1    1    1
[3,]    1    1    0    1
[4,]    1    1    0    1
[5,]    1    1    0    1
[6,]    0    1    0    1
[7,]    0    1    0    1
[8,]    0    1    0    1
[9,]    0    1    0    1

I want to store the values (4 0 7 0) in unSpells. That is the values
that represent the "last" sequence of zeros (that is I want to ignore
other possible zeros like the ones I have inserted above).

thanks!
Mario



Dimitris Rizopoulos wrote:
> it's not totally clear to me what exactly do you need in this case, 
> but have a look at the following:
>
> Atr <- cbind(rep(1:0, each = 4), 1, c(1, rep(0, 7)), 1)
> unSpells <- colSums(Atr == 0)
> unSpells[unSpells == 0] <- 1
> unSpells
>
>
> I hope it helps.
>
> Best,
> Dimitris
>
>
> Mario Lavezzi wrote:
>> Hello,
>> I have the following problem.
>>
>> I am running simulations on possible states of a set of agents 
>> (1=employed, 0=unemployed).
>>
>> I store these simulated time series in a matrix like the following, 
>> where rows indicates time periods, columns the number of agents (4 
>> agents and 8 periods in this case):
>>
>> Atr=[
>> 1    1    1    1
>> 1    1    0    1
>> 1    1    0    1
>> 1    1    0    1
>> 0    1    0    1
>> 0    1    0    1
>> 0    1    0    1
>> 0    1    0    1]
>>
>> At this point, I need to update a vector ("unSpells") which contains 
>> the lenghts of unemployment spells, and is initialized with ones. 
>> Practically, in the case represented I need to store the value "4" at 
>> position 1 of unSpells and "7" at position 3 of unSpells (that is, I 
>> care only of those who, in the last row, are zeros).
>>
>> I am doing this in the following way (tt+1 indicates the time period 
>> reached by the simulation, n the number of agents):
>>
>>    unSpells = matrix(1,nrow=1,ncol=n)      
>> ppp=apply(Atr[1:(tt+1),],2,rle)
>>    for(i in (1:n)[Atr[tt+1,]==0]){
>>        unSpells[i]=tail(ppp[[i]]$lengths,1)
>>    }
>>
>> It works, but the for (i in ...) loop slows down the simulation a lot.
>>
>> Any suggestion on how to avoid this loop? (or in general, to speed up 
>> this part of the simulation)
>>
>> Thanks!!
>> Mario
>>
>

-- 
Andrea Mario Lavezzi
Dipartimento di Studi su Politica, Diritto e Società
Università di Palermo
Piazza Bologni 8
90134 Palermo, Italy
tel. ++39 091 6625600
fax ++39 091 6112023
skype: lavezzimario
email: lavezzi (at) unipa.it
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