I have created simulated data for a mixed logit model. It involves N anglers taking two trips, each of which can be to one of two sites. Here is the code to create the simulated data:
library(data.table)
library(mlogit)
### Angler choice probabilities for site a
N <- 1e4
beta <- rnorm(N, mean = 0.5)
val <- runif(N)
p <- exp(1 + beta*val)/(1+ exp(1 + beta*val))
### Choice for trip 1
Y11 <- rbinom(N, 1, p)
Y10 <- 1 - Y11
### Choice for trip 2
Y21 <- rbinom(N, 1, p)
Y20 <- 1 - Y21
### Data set
id <- as.character(1:N)
sim <- data.table(angler = rep(id, 4),
trip = paste(id, rep(1:2, each = 2*N), sep = "_"),
site = c(rep(letters[1:2], each = N),
rep(letters[1:2], each = N)),
is_choice = as.logical(c(Y11, Y10, Y21, Y20)),
term = c(val, rep(0, N), val, rep(0, N)))
sim[, term2 := ifelse(site == "a", 1, 0)]
When I run mlogit, I get the following error:
> mlogit(is_choice ~ 1, sim, shape = "long", alt.var = "site", chid.var = "trip", id.var = "angler")
Error in str2lang(x) : <text>:2:0: unexpected end of input
1: . ~ . |
^
I can run examples from the vignette, so there doesn't seem to be an installation issue.
What am I fouling up? Thanks!
This problem can be solved by using data.frame, not data.table.
sim2 <- as.data.frame(sim)
mlogit(is_choice ~ 1, sim2, shape = "long", alt.var = "site", chid.var = "trip", id.var = "angler")
Call:
mlogit(formula = is_choice ~ 1, data = sim2, shape = "long", alt.var = "site", chid.var = "trip", id.var = "angler", method = "nr")
Coefficients:
(Intercept):b
-1.1595