dfidx(
  data,
  idx = NULL,
  drop.index = TRUE,
  as.factor = NULL,
  pkg = NULL,
  fancy.row.names = FALSE,
  subset = NULL,
  idnames = NULL,
  shape = c("long", "wide"),
  choice = NULL,
  varying = NULL,
  sep = ".",
  opposite = NULL,
  levels = NULL,
  ranked = FALSE,
  ...
)

data("TravelMode", package = "AER")

# the first two columns contain the index

TM1 <- dfidx(TravelMode)

# explicitely indicate the two indexes using either a vector or a
# list of two characters

TM2 <- dfidx(TravelMode, idx = c("individual", "mode"))

TM3 <- dfidx(TravelMode, idx = list("individual", "mode"))

# rename one or both indexes

TM3b <- dfidx(TravelMode, idnames = c(NA, "trmode"))

# for balanced data (with observations ordered by the first, then
# by the second index

# use the name of the first index

TM4 <- dfidx(TravelMode, idx = "individual", idnames = c("individual", "mode"))

# or an integer equal to the cardinal of the first index

TM5 <- dfidx(TravelMode, idx = 210, idnames = c("individual", "mode"))

# Indicate the values of the second index using the levels argument

TM5b <- dfidx(TravelMode, idx = 210, idnames = c("individual", "mode"),
levels = c("air", "train", "bus", "car"))

# Nesting structure for one of the index

data("JapaneseFDI", package = "mlogit")
JapaneseFDI <- dplyr::select(JapaneseFDI, 1:8)
JP1b <- dfidx(JapaneseFDI, idx = list("firm", c("region", "country")),
idnames = c("japf", "iso80"))

# Data in wide format

data("Fishing", package = "mlogit")
Fi <- dfidx(Fishing, shape = "wide", varying = 2:9, idnames = c("chid", "alt"))