Stochastic array of multinomial logistic regression parameter fits

probs.logit

probs.logit <- function(grps.seq, cov, coeff, x){
  ##
  ## multinomial logistic regression model fit for a given covariate
  ## e.g. probability sums per age =1
  ##
  ## x: covariate value e.g. age=16
  ## grps: vector of class labels for NATSAL groups e.g. het5yrs
  ## cov: covariate name to regress against (string)
  ## coeff: coefficients from the mlogit() fit
  
  ## likleihood
  L <- pihat <- vector()
  L[1] <- 0
  
  for(i in grps.seq[-1]){
    ## omit pivot group from loop
    
    intercept <- paste(i, ":(intercept)", sep="")
    cov_index <- paste(i, ":", cov, sep="")
    L[which(grps.seq==i)] <- coeff[intercept] + coeff[cov_index]*x
  }
  denom <- sum(exp(L))
  
  for (i in 1:length(L)){
    pihat[i] <- exp(L[i])/denom
  }
  names(pihat) <- grps.seq
  
  pihat
}
## END FUNCTION ##