Adding additional values to tables in Lua

Question

I have a input file with different food types

Corn Fiber 17
Beans Protein 12
Milk Protien 15
Butter Fat 201
Eggs Fat 2
Bread Fiber 12
Eggs Cholesterol 4
Eggs Protein 8
Milk Fat 5

(Don't take these too seriously. I'm no nutrition expert) Anyway, I have the following script that reads the input file then puts the following into a table

    file = io.open("food.txt")
foods = {}
nutritions = {}
for line in file:lines() 
    do
        local f, n, v = line:match("(%a+) (%a+) (%d+)")
        nutritions[n] = {value = v}
        --foods[f] = {} Not sure how to implement here
    end
file:close()

(It's a little messy right now) Notice also that different foods can have different nutrients. For example, eggs have both protein and fat. I need a way to let the program, know which value I am trying to call. For example:

> print(foods.Eggs.Fat)
2
> print(foods.Eggs.Protein
8

I believe I need two tables, as shown above. The foods table will contain a table of nutritions. This way, I can have multiple food types with multiple different nutrient facts. However, I am not sure how to handle a table of tables. How can I implement this within my program?

Yu Hao · Accepted Answer · 2017-03-29 06:01:12Z

2

The straightforward way is to test if food[f] exists, to decide whether to create a new table or add elements to existing one.

foods = {}
for line in file:lines() do
    local f, n, v = line:match("(%a+) (%a+) (%d+)")
    if foods[f] then
        foods[f][n] = v
    else
        foods[f] = {[n] = v}
    end
end

answered Mar 29, 2017 at 6:01

Yu Hao

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