How do I detect the most common value in a table?
For Context: I am making a raid system for a clan that detects a common group between all the raiders.
My Procedure: Basically, I use GroupService to get all the groups that each player in-game is in; then I add the group names to a table.
In order to predict which group is raiding, I want to find which string (the group name) is the most common in the table. In essence, the mode of the data.
My question is, what function would I use to figure out the mode? Is there a default ROBLOX function for this? If not, how can I make one myself?
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1 answer
There is no built-in function to do this (the Lua standard library is very bare, and ROBLOX doesn't really add anything that deals with plain types like tables)
Here's an outline of how you might do it:
Given your list, build a map count where count[value] is the number of times that value appeared in list.
Implementation
01 | -- returns a `counts` map such that `counts[value]` |
02 | -- is the number of times that `value` appears in `list` |
03 | function countMap(list) |
04 | local counts = {} |
05 | for _, value in ipairs(list) do |
06 | if counts[value] then |
07 | -- 2nd or on time that we've seen this element |
08 | counts[value] = counts[value] + 1 |
09 | else |
10 | -- 1st time we've seen this element |
11 | counts[value] = 1 |
12 | end |
13 | end |
14 | return counts |
15 | end |
This can be shortened a bit, if you want:
01 | -- returns a `counts` map such that `counts[value]` |
02 | -- is the number of times that `value` appears in `list` |
03 | function countMap(list) |
04 | local counts = {} |
05 | for _, value in ipairs(list) do |
06 | -- "default" counts[value] to 0 if it's not already there |
07 | counts[value] = (counts[value] or 0) + 1 |
08 | end |
09 | return counts |
10 | end |
After we have the counts, we just need to find the key that has the largest value.
01 | -- returns a `key` such that `map[key]` is as large as possible |
02 | function keyLargest(map) |
03 | local best = nil |
04 | for key in pairs(map) do |
05 | if best == nil then |
06 | -- first key in the map |
07 | best = key |
08 | elseif map[best] < map[key] then |
09 | -- `key` has a bigger value than `best`, |
10 | -- so `key` is our new best |
11 | best = key |
12 | end |
13 | end |
14 | return best |
15 | end |
This can be shortened a bit, if you want:
01 | -- returns a `key` such that `map[key]` is as large as possible |
02 | function keyLargest(map) |
03 | local best = next(map) -- get an arbitrary key |
04 | for key in pairs(map) do |
05 | if map[best] < map[key] then |
06 | best = key |
07 | end |
08 | end |
09 | return best |
10 | end |
Then mostCommon can just be defined in terms of the above two functions:
1 | -- returns an element that appears the most number of times in `list` |
2 | function mostCommon(list) |
3 | return keyLargest(countMap(list)) |
4 | end |
Note that this will break ties arbitrarily, i.e., mostCommon{1, 1, 2, 2} could be either 1 or 2.