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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I was testing some R code in Chapter 13 on Choice Based Conjoint. I was going through the step by step introduction you have that creates the
<b><u>cbc.df</u></b> data file from scratch. Here is the code (<i>in italics</i>) I have so far when the following error cropped up<b>: Error in nrow(profiles) : object 'profiles' not found</b> (please see the
<span style="background:yellow;mso-highlight:yellow">highlighted code</span> at the end of the code section in the email below). What is causing the error?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thanks for your help.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Sri<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif""><o:p> </o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">attrib <- list(seat = c("6", "7", "8"),<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">cargo = c("2ft", "3ft"),<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">eng = c("gas", "hyb", "elec"),<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">price = c("30", "35", "40"))<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif""><o:p> </o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">coef.names <- NULL<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">for (a in seq_along(attrib)) {<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">coef.names <- c(coef.names,<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">paste(names(attrib)[a], attrib[[a]][-1], sep=""))<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">}<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif""><o:p> </o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">coef.names<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif""><o:p> </o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">mu <- c(-1, -1, 0.5, -1, -2, -1, -2)<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">names(mu) <- coef.names<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">mu<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif""><o:p> </o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">Sigma <- diag(c(0.3, 1, 0.1, 0.3, 1, 0.2, 0.3))<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">dimnames(Sigma) <- list(coef.names, coef.names)<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">Sigma["enghyb", "engelec"] <- Sigma["engelec", "enghyb"] <- 0.3<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif""><o:p> </o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">set.seed(33040)<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">resp.id <- 1:200 # respondent ids<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">carpool <- sample(c("yes", "no"), size=length(resp.id), replace=TRUE, prob=c(0.3, 0.7))<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif""><o:p> </o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">library(MASS)<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">coefs <- mvrnorm(length(resp.id), mu=mu, Sigma=Sigma)<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">colnames(coefs) <- coef.names<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif""><o:p> </o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">coefs[carpool=="yes", "seat8"] <- coefs[carpool=="yes", "seat8"] + 2<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">coefs[carpool=="yes", "seat7"] <- coefs[carpool=="yes", "seat7"] + 1.5<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif""><o:p> </o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">head(cbind(carpool, coefs))<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif""><o:p> </o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">nques <- 15<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">nalt <- 3<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif""><o:p> </o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">profiles <- expand.grid(attrib)<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">nrow(profiles)<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">head(profiles)<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif""><o:p> </o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">profiles.coded <- model.matrix(~ seat + cargo + eng + price, data=profiles)[ , -1]<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">head(profiles.coded)<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif""><o:p> </o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">cbc.df <- data.frame(NULL)<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">for (i in seq_along(resp.id)) {<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif";background:yellow;mso-highlight:yellow">profiles.i <- sample(1:nrow(profiles), size=nques*nalt)</span></i><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif""><o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">utility <- profiles.coded[profiles.i, ] %*% coefs[i, ]<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">wide.util <- matrix(data=utility, ncol=nalt, byrow=TRUE)<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">probs <- exp(wide.util) / rowSums(exp(wide.util))<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">choice <- apply(probs, 1, function(x) sample(1:nalt, size=1, prob=x))<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">choice <- rep(choice, each=nalt)==rep(1:nalt, nques)<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">conjoint.i <- data.frame(resp.id=rep(i, nques),<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">ques = rep(1:nques, each=nalt),<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">alt = rep(1:nalt, nques),<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">carpool = rep(carpool[i], nques),<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">profiles[profiles.i, ],<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">choice = as.numeric(choice))<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">cbc.df <- rbind(cbc.df, conjoint.i)<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif""># Tidy up, keeping only cbc.df and attrib<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">rm(a, i, resp.id, carpool, mu, Sigma, coefs, coef.names,<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">conjoint.i, profiles, profiles.i, profiles.coded, utility,<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">wide.util, probs, choice, nalt, nques)<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif"">}<o:p></o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif""><o:p> </o:p></span></i></p>
<p class="MsoNormal"><i><span style="font-size:12.0pt;font-family:"Arial","sans-serif""><o:p> </o:p></span></i></p>
<p class="MsoNormal"><o:p> </o:p></p>
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