Lua how to access specific data in a nested table - lua

Question

I parsed some data from a CSV file to a Lua table.
Lets say the table looks like this just bigger
tab {
{ id = 1761, anotherID=2, ping=pong}
{ id = 2071, anotherID=4, ping=notpong}
}
Now I want to know every ID (without displaying any other data yet) to store them in another table for some time.
I am completely lost here for now..
Using what you wrote I rewrote it a bit and went to have:
minitab = {}
for i, value in ipairs(tab) do
local id = value.id
local anotherID = value.anotherID
minitab[id] = anotherID
end
Would that work? In fact i later want to get just 2 values of a way larger array (around 30 datas) - but I can only push a single array to a GUI dropdown. I want to save the ID as a key and the "anotherID" value wich will be a text after that key so if a ask for the 2071st value it displays the "name" 4

Answer 1

The code below stores the ids as keys in another table:
id={}
for k,v in ipairs(tab) do
id[v.id]=true
end
You can then traverse id with pairs to list the ids.
If you want to remember where each id came from, use id[v.id]=k in the loop.

Answer 2

Based on your question, you can use this code to traverse your data table tab and get minitab to be used for your GUI array:
--data
tab = {
{id = "4204", label = "2", desc = "Roancyme"},
{id = "5517", label = "9", desc = "Bicktuft"},
{id = "1035", label = "3", desc = "Pipyalum"},
}
--temporary table
local minitab = {}
for i, option in ipairs(tab) do
minitab[option.id] = option.label
end
--print minitab
print('<select>')
for id, label in pairs(minitab) do
print(string.format('<option value="%s">%s</option>', id, label)) --> <option value="1035">3</option>
end
print('</select>')
print()
However, I don't think it is necessary to create a temporary table to store those values, because you can easily traverse your original table tab and directly pull out the output you need; like this:
--print directly from tab
print('<select>')
for i, option in ipairs(tab) do
print(string.format('<option value="%s">%s</option>', option.id, option.label)) --> <option value="1035">3</option>
end
print('</select>')
print()
Unless you need to work with it before displaying the list on the drop down (e.g. add some prefix to the label, sort minitab by the label, etc); but you don't want to disturb the original data table tab. In this case, it would make sense to use the temporary table.
--format values in temporary table
local minitab = {}
for i, option in ipairs(tab) do
local minitabID = option.id
local minitabLabel = string.format('Item %s - %s', option.label, option.desc)
table.insert(minitab, {id = minitabID, label = minitabLabel})
end
--sort temporary table
table.sort(minitab, function (o1, o2) return o2.label > o1. label end)
--print formatted values from temporary table
print('<select>')
for i, option in ipairs(minitab) do
print(string.format('<option value="%s">%s</option>', option.id, option.label)) --> <option value="4204">Item 2 - Roancyme</option>
end
print('</select>')
NB: Please take a note on which table iteration uses ipairs and which one uses pairs. See the complete code snippet here.