[R] if value is in vector, perform this function

[Patrick Burns]

I forgot to say:

Also do not depend on equality in this situation.
You want to test equality with a tolerance.

See Circle 1 of 'The R Inferno':
http://www.burns-stat.com/documents/books/the-r-inferno/

I also see that 't' is a vector unlike what I was
thinking before, thus you want to use 'ifelse':

C_A <- ifelse(t %in% feed_days, 1.5, 0)

except that still leaves out the tolerance.  If
you are always only going to go by half-days, then
the following should work:

C_A <- ifelse( round(2*t) %in% round(2 * feed_days), 1.5, 0)

Pat

On 02/03/2013 23:57, Louise Stevenson wrote:
> Hi,
>
> I'm trying to set up R to run a simulation of two populations in which every 3.5 days, the initial value of one of the populations is reset to 1.5. I'm simulation an experiment we did in which we fed Daphnia populations twice a week with algae, so I want the initial value of the algal population to reset to 1.5 twice a week to simulate that feeding. I've use for loops and if/else loops before but I can't figure out how to syntax "if t is in this vector of possible t values, do this command, else, do this command" if that makes sense. Here's what I have (and it doesn't work):
>
> params = c(1, 0.15, 0.164, 1)
> init = c(1.5, 0.05)
> t=seq(1,60, by=0.5) #all time values, experiment ran for 60 days
>
> #feeding sequence - every "3.5 days"
> feed_days = seq(1,60,by=3.5)
>
> Daphnia <- function(t,x,params){
> 	C_D = x[2];
> 	C_A = 0;
> 	for(t %in% feed_days){
> 		if t == TRUE {
> 		C_A = 1.5
> 		}
> 	else{
> 		C_A = 0
> 	 }}
> 	gamma = params[1]; m_D = params[2]; K_q = params[3]; q_max = params[4];
> 	M_D = m_D * C_D
> 	I_A = (C_D * q_max * C_A) / (K_q + C_A)
> 	r_D = gamma * I_A
> 	return(
> 	list(c(
> 	 - I_A,
> 	r_D - M_D
> 	)))
> 	}
>
> library(deSolve)
> results <- ode(init, t, Daphnia, params, method = "lsoda")
>
>
> Let me know if there's any other info that would be helpful and thanks very much for your help!
>
>
> 	[[alternative HTML version deleted]]
>
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-- 
Patrick Burns
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