Table search?

[TheConfuZzledDude]

This may be a nooby question, but how do you check if something is part of a certain table?

[kikito]

It depends on two things: 1. How things are "be part of the table" (there are several ways) and 2. What you know.

Everything inserted in a table can be retrieved using its key. So if you know the key, you can do this:

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if t[keyOfSomething] == nil then
  -- something is not inside of t
else
  -- something is inside of t
end

If you don't know the key, you can parse the table and check the values one by one, like this:

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function contains(t, something)
  for _,v in pairs(t) do
    if v == something then return true end
  end
  return false
end

And you can use the function like this:

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if contains(t, something) then
  -- t contains something
else
  -- t does not contain something
end

This option is kindof slow, but always works. You can do optimizations in the for loop (i.e. using a numerical index instead of pairs, if you know that t is an array-like table), but if you are going to be calling contains very often on a table you might as well use the third option.

The third option relies on one very special property of tables - the keys of a table can be anything, not just numbers or strings. So when inserting stuff on the table, instead of using an array-like table, like this:

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t[#t + 1] = something -- adding something to t, as in an array

You can use "something" as the key, like this:

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t[something] = true -- adding something to t, as a key

And now knowing wether something is inside t is very simple:

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if t[something] then
  -- something is inside of t
else
  -- something is not inside of t
end

Notice that you don't need to know the key of something here - because something is the key already.

This kind of table is faster for "checking up if stuff exists", but it's a bit slower for "parsing all the elements", since you can't use a numeric for, as you can in array-like tables. So it's a bit of a tradeoff. If you are going to be looking up stuff all the time in a table, use the third option. If you are going to be parsing all the elements in the table (i.e. to draw all the enemies on the screen, you must parse them all), use an array.

[spir]

This may be a nooby question, but how do you check if something is part of a certain table?

Please, say the topic of your help request in the title (help others help you).

Denis

[TheConfuZzledDude]

This may be a nooby question, but how do you check if something is part of a certain table?

Please, say the topic of your help request in the title (help others help you).

Denis

Sorry about that, changed the topic name.

It depends on two things: 1. How things are "be part of the table" (there are several ways) and 2. What you know.

Everything inserted in a table can be retrieved using its key. So if you know the key, you can do this:

This kind of table is faster for "checking up if stuff exists", but it's a bit slower for "parsing all the elements", since you can't use a numeric for, as you can in array-like tables. So it's a bit of a tradeoff. If you are going to be looking up stuff all the time in a table, use the third option. If you are going to be parsing all the elements in the table (i.e. to draw all the enemies on the screen, you must parse them all), use an array.

OK, I think I get that. So if I had a table where I loaded all of a certain type of objects, and I wanted to check if the object my player was colliding with was in one of these tables, and this was continuous, which method would I use?

[kikito]

OK, I think I get that. So if I had a table where I loaded all of a certain type of objects, and I wanted to check if the object my player was colliding with was in one of these tables, and this was continuous, which method would I use?

If they are only ever going to be "checked against the player", then an array type will do. If you think you will need to check the same collisions for other things (like bullets, platforms, etc) then use option 3.

[TheConfuZzledDude]

OK, I think I get that. So if I had a table where I loaded all of a certain type of objects, and I wanted to check if the object my player was colliding with was in one of these tables, and this was continuous, which method would I use?

If they are only ever going to be "checked against the player", then an array type will do. If you think you will need to check the same collisions for other things (like bullets, platforms, etc) then use option 3.

OK, so I can now check if a certain object is inside that table, but how do I actually check if the object the player is colliding with is in the table?

[kikito]

OK, so I can now check if a certain object is inside that table, but how do I actually check if the object the player is colliding with is in the table?

You literally do this:

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if theTable[theObject] then
  -- the table contains the object
else
  -- the table does not contain the object
end