# Simple Stats

This is a small set of functions to do some statistics (e.g. mean, mode, median, standard deviation, and min/max) on tables. Just fill your tables with numbers and call the function you want. I haven't optimised these at all.

All function except `mode` will skip over any non-numeric data and also the table does not have to be indexed. E.g.

```t = {[1]=5, [2]=7, [3]=8, [4]='Something else.'}  -- or
t = {["a"]=5, ["b"]=7, ["c"]=8, ["name"]='My table of numbers'}
```

is fine for input to these. Note that the 'Mode' function is slightly different. It works on anything, not just numbers.

```-- Small stats library                      --
----------------------------------------------
-- Version History --
-- 1.0 First written.

-- Tables supplied as arguments are not changed.

-- Table to hold statistical functions
stats={}

-- Get the mean value of a table
function stats.mean( t )
local sum = 0
local count= 0

for k,v in pairs(t) do
if type(v) == 'number' then
sum = sum + v
count = count + 1
end
end

return (sum / count)
end

-- Get the mode of a table.  Returns a table of values.
-- Works on anything (not just numbers).
function stats.mode( t )
local counts={}

for k, v in pairs( t ) do
if counts[v] == nil then
counts[v] = 1
else
counts[v] = counts[v] + 1
end
end

local biggestCount = 0

for k, v  in pairs( counts ) do
if v > biggestCount then
biggestCount = v
end
end

local temp={}

for k,v in pairs( counts ) do
if v == biggestCount then
table.insert( temp, k )
end
end

return temp
end

-- Get the median of a table.
function stats.median( t )
local temp={}

-- deep copy table so that when we sort it, the original is unchanged
-- also weed out any non numbers
for k,v in pairs(t) do
if type(v) == 'number' then
table.insert( temp, v )
end
end

table.sort( temp )

-- If we have an even number of table elements or odd.
if math.fmod(#temp,2) == 0 then
-- return mean value of middle two elements
return ( temp[#temp/2] + temp[(#temp/2)+1] ) / 2
else
-- return middle element
return temp[math.ceil(#temp/2)]
end
end

-- Get the standard deviation of a table
function stats.standardDeviation( t )
local m
local vm
local sum = 0
local count = 0
local result

m = stats.mean( t )

for k,v in pairs(t) do
if type(v) == 'number' then
vm = v - m
sum = sum + (vm * vm)
count = count + 1
end
end

result = math.sqrt(sum / (count-1))

return result
end

-- Get the max and min for a table
function stats.maxmin( t )
local max = -math.huge
local min = math.huge

for k,v in pairs( t ) do
if type(v) == 'number' then
max = math.max( max, v )
min = math.min( min, v )
end
end

return max, min
end
```

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Last edited July 4, 2008 4:56 pm GMT (diff)