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I am implementing a multinomial logit model using the mlogit package in R. The data includes three different "choices" and three variables (A, B, C) which contains information for the independent variable. I have transformed the data into a wide format using the mlogit.data function which makes it look like this: 

Observation  Choice  VariableA  VariableB   VariableC
     1          1         1.27       0.2         0.81        
     1          0         1.27       0.2         0.81           
     1         -1         1.27       0.2         0.81 
     2          1         0.20       0.45        0.70
     2          0         0.20       0.45        0.70      
     2         -1         0.20       0.45        0.70

The thing is that I want the independent variable to be choice-specific and therefore being constructed as Variable D below: 

   Observation  Choice  VariableA  VariableB  VariableC  VariableD
     1          1         1.27       0.2         0.81        1.27
     1          0         1.27       0.2         0.81        0.2
     1         -1         1.27       0.2         0.81        0.81
     2          1         0.20       0.45        0.70        0.20
     2          0         0.20       0.45        0.70        0.45
     2         -1         0.20       0.45        0.70        0.70

Variable D was constructed using the following code: 

choice_map <- data.frame(choice = c(1, 0, -1), var = grep('Variable[A-C]', names(df)))

df$VariableD <- df[cbind(seq_len(nrow(df)), with(choice_map, var[match(df$Choice, choice)]))]

However, when I try to run the multinomial logit model, 

mlog <- mlogit(Choice ~ 1 | VariableD, data=df, reflevel = "0")

the error message "row names supplied are of the wrong length" is returned. When I use any of the other variables A-C separately the regression is run without any problems, so my questions are therefore: why can't Variable D be used and how can this problem be solved?

Thanks!

carsentdum
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  • Sorry, there should be no spaces – carsentdum Feb 26 '19 at 19:32
  • it looks like `mlogit` is expecting the df to have an attribute `index`. It's not clear where that is meant to come from though. using the source of `mlogit:::"[.mlogit.data"` we see: `index <- \`[.data.frame\`(attr(x, "index"), i, )`; `index <- data.frame(lapply(index, function(x) x[drop = TRUE]), row.names = rownames(mydata)) ` which is what is causing the error – Ricardo Saporta Feb 26 '19 at 19:38
  • is `df` a standard data.frame? or is it an mlogit object? It's possible that when adding VariableD, the object is getting coerced – Ricardo Saporta Feb 26 '19 at 19:40
  • df is an mlogit object from the mlogit.data function – carsentdum Feb 26 '19 at 20:03

1 Answers1

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I got this error when I entered my original dataframe into the model, and not the wide dataframe created by mlogit.data. So make sure to create your "wide" dataframe first and enter this into your mlogit function. (source: Andy Field, Discovering statistics using R, page 348)

new_in_R
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