R error: dims do not match the length of an object - r

I am currently trying to run some code (if you need to know the purpose to help me, ask me, but I'm trying to keep this question short). This is the code:
par<-c(a=.5,b=rep(1.3,4))
est<-rep(TRUE,length(par))
ncat<-5
Theta<-matrix(c(-6,-5.8,-5.6,-5.4,-5.2,-5,-4.8,-4.6,-4.4,-4.2,-4,-3.8,-3.6,-3.4,-3.2,-3,-2.8,-2.6,-2.4,-2.2,-2,-1.8,-1.6,-1.4,-1.2,-1,-0.8,-0.6,-0.4,-0.2,0,0.2,0.4,0.6,0.8,1,1.2,1.4,1.6,1.8,2,2.2,2.4,2.6,2.8,3,3.2,3.4,3.6,3.8,4,4.2,4.4,4.6,4.8,5,5.2,5.4,5.6,5.8,6))
p.grm<-function(par,Theta,ncat){
a<-par[1]
b<-par[2:length(par)]
z<-matrix(0,nrow(Theta),ncat)
y<-matrix(0,nrow(Theta),ncat)
y[,1]<-1
for(i in 1:ncat-1){
y[,i+1]<-(exp(a*(Theta-b[i])))/(1+exp(a*(Theta-b[i])))
}
for(i in 1:ncat-1){
z[,i]<-y[,i]-y[,i+1]
}
z[,ncat]<-y[,ncat]
z
}
However, when I try to run the code:
p.grm(par=par,Theta=Theta,ncat=ncat)
I get the following error:
Error: dims [product 61] do not match the length of object [0]
Traceback tells me that the error is occurring in the first for loop in the line:
y[,i+1]<-(exp(a*(Theta-b[i])))/(1+exp(a*(Theta-b[i])))
Could someone point me to what I'm doing wrong? When I try to run this code step by step outside of the custom p.grm function, everything seems to work fine.

It is a common mistake. When you write the for loop and you want it from 1 to ncat -1 remember to write it as for (i in 1:(ncat-1)) instead of for(i in 1:ncat-1) they are completly different.
You may also add to the function something to return return(z). Here it is the corrected code:
par<-c(a=.5,b=rep(1.3,4))
est<-rep(TRUE,length(par))
ncat<-5
Theta<-matrix(c(-6,-5.8,-5.6,-5.4,-5.2,-5,-4.8,-4.6,-4.4,-4.2,-4,-3.8,-3.6,-3.4,-3.2,-3,-2.8,-2.6,-2.4,-2.2,-2,-1.8,-1.6,-1.4,-1.2,-1,-0.8,-0.6,-0.4,-0.2,0,0.2,0.4,0.6,0.8,1,1.2,1.4,1.6,1.8,2,2.2,2.4,2.6,2.8,3,3.2,3.4,3.6,3.8,4,4.2,4.4,4.6,4.8,5,5.2,5.4,5.6,5.8,6))
p.grm<-function(par,Theta,ncat){
a<-par[1]
b<-par[2:length(par)]
z<-matrix(0,nrow(Theta),ncat)
y<-matrix(0,nrow(Theta),ncat)
y[,1]<-1
for(i in 1:(ncat-1)){
y[,i+1]<-(exp(a*(Theta-b[i])))/(1+exp(a*(Theta-b[i])))
}
for(i in 1:(ncat-1)){
z[,i]<-y[,i]-y[,i+1]
}
z[,ncat]<-y[,ncat]
return(z)
}
p.grm(par=par,Theta=Theta,ncat=ncat)

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Create a series of new folders in for loop in R

I have create a small script that passes a vector through a loop. In this loop I am using an if else statement to check if folder exists and if not to create the folder. However, I am getting error: Error in file.exists(i) : invalid 'file' argument. This has to due with file.exist(). I dont understand why this isnt ok. I check the man using help. Seems like this should be working.
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You are looping over an index (that is, 1:length(folders) is just the vector 1:7, not the values of the folders vector itself. The easiest solution is to loop over the vector itself:
for (i in folders) {
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I have a small testing program that uses testthat
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The code is from this blog -http://giventhedata.blogspot.in/2012/08/r-and-web-for-beginners-part-iii.html.
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dreg=read.csv("dayreg.csv")
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https://stats.stackexchange.com/questions/20653/vector-multiplication-in-bugs-and-jags/20739#20739
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