# [R] help with population matrix

John Kane jrkrideau at inbox.com
Mon Feb 18 17:49:51 CET 2013

```Currently your code does not seem to make any sense

John Kane

> -----Original Message-----
> From: sf62 at st-andrews.ac.uk
> Sent: Mon, 18 Feb 2013 16:09:49 +0000
> To: r-help at r-project.org
> Subject: [R] help with population matrix
>
> Hi guys, I am a biologist and an R newbie, and I'm learning how to create
> a
> simple population model.
>
> So, I have a population matrix ("pop")of 30 age classes of female (1:4
> are
> non-breeders, 5:30 are breeders) which will be modelled for 100 years.
>
>> pop <- matrix(0,30,100)
>
> I then populate this matrix with 3 young adult females.
>
>> pop[5, 1] <- 3

What is this expected to do?
>
> I then want to run this for 100 years, with stochasticity, to see how
> this
> population does over time.
>
>> for (y in 1:100)  {
>>     pop[1,t+1] <- rbinom(1,colSums(pop[5:30, t]), b/2)
>
> (I haven't filled these in but you don't need them, they all have
> different
> survival probabilities to the sexually-mature adults.)
>
>>    pop[5, t+1] <- rbinom(1, pop[4, t], s2)
>>    pop[6, t+1] <- rbinom(1, pop[5, t], s2)
> .....
>>    pop[30, t+1] <- rbinom(1, pop[29, t], s2)
> }
>
What is t , s2 b etc?

> So my question is: is there any way of populating this matrix without
> having to explicitly write 30 lines of code? Because lines 5 - 30 are all
> going to be the same, and yet even after 5 hours (literally) of web
> searching and R manual reading I can't find a way to index the rows,
> which
> seems to be what's needed here.
>
> Any insight is welcome here, including a different way of modelling this
> population.
> Many thanks, Sam.

This may be one of the cases where it really is better to have some detailed explanation of what you want rather than how to code it.

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