Is there a more efficient way to simulate in R, by exposition factor, gender and disease profile?

Question

I started working with R recently and need to do a simulation for 100 000 people that divides them in exposition factor for a disease, gender and presence or absence of disease. My background info is that the probability of being exposed to this risk factor is 0.15 in this population. The probability of being a woman, among exposed people is 0.2 and among non exposed people is 0.5. I also know that there are 4 gamma distributions - divided by gender and exposition factor - that characterize the disease. If X> 35, from each gamma, then you have the disease. I used the following code to answer this question:

n<-100000
exposition<-rep(0,n) 
#vector that represents non exposed ("non exposed" = 1, "exposed" = 0)
gender<-rep(0,n) #vector that reprsents gender ("women" = 1, "men" = 0)
disease<-rep(0,n) 
#vector that represents disease ("with disease" = 0, "without disease" = 1)
u<-runif(n,0,1)
b<-runif(n,0,1)
c<-runif(n,0,1)

#in 100 000 cases atributes non expostion
for(i in 1:n){if(u[i]>0.15)exposicao[i]<-1}

#cycle that determines the gender of the subjects
for(j in 1:n){{if(exposicao[j]==1 & b[j]>0.5)genero[j]<-1} 
{if(exposicao[j]==0 & b[j]<0.2)genero[j]<-1}} 

#Cycle that determines the state of disease from the subjects. I define people with
disease as people with c[x] inferior to the probability of having the disease
(P(X>35)), according to their gamma distribution. I used the results from that
calculation.

     for(x in 1:n){{if(expositon[x]==1 & gender[x]==1 & c[x]<0.06840084)doentes[x]<-1} 
 #if the person is non exposed and woman X2~G(12,2)
 {if(exposition[x]==0 & gender[x]==1 & c[x]<0.1698673)doentes[x]<-1} 
 #if it's exposed and woman X3~G(14,2)
 {if(exposicao[x]==1 & genero[x]==0 & c[x]<0.02010428)doentes[x]<-1} 
 #if it's non exposed and man X1~G(10,2)
 {if(exposicao[x]==0 & genero[x]==0 & c[x]<0.3275424)doentes[x]<-1}}
 #if it's exposed and man X4~G(16,2)

Answer 1

There are a few improvements to your (I'm assuming that genero and gender are the same variable).

1. Very important. Use a space around the assignment operator! x<-5 Does this mean assign 5 to x to is x less than -5
2. Rather then rep(0,n) just use numeric(n)

3. Your loops should be rewritten. For example:

   ##I presume that exposicao is exposition.
   for(i in 1:n){if(u[i]>0.15)exposicao[i]<-1}
   

   can be written as:

   exposition[runif(n) > 0.15] = 1
   

   and

   for(j in 1:n){{if(exposicao[j]==1 & b[j]>0.5)genero[j]<-1} 
   {if(exposicao[j]==0 & b[j]<0.2)genero[j]<-1}} 
   

   can be written as:

   genero[exposicao==1 & b>0.5] = 1
   genero[exposicao==0 & b>0.2] = 1