Define empty or uninitialized columns in Julia IndexedTables ndsparse

[dmikushin]

Hello, I'm cross-posting this from SO, in hope to get an answer.

I'm defining NDSparse table, with two columns "state" and "action" that shall be filled later. How should I specify these columns upon initialization?

using Pkg
Pkg.add("IndexedTables")
using IndexedTables

start_period = 1        # numer of first period to consider
num_agents = 100        # number of individuals to simulate

periods = [start_period, start_period + 3]

# https://github.com/JuliaData/IndexedTables.jl
df = ndsparse((Identifier = [1, num_agents], Period = periods), (state = [???], action = [???]))
print(df)

Furthermore, while "action" is an integer, "state" is supposed to be an integer array of a variable length.