## manhattan distance

### Data

in lua

#### Tags

length, manhattan, mathematics

### Source Code

``````-- Manhattan distance distance implementation
-- See: http://en.wikipedia.org/wiki/Manhattan_distance

-- Returns the Manhattan distance between two vectors
-- p       : a first vector
-- q       : a second vector
-- returns : the distance between p and q
local function manhattan_distance(p, q)
assert(#p == #q, 'vectors must have the same length')
local s = 0
for i in ipairs(p) do
s = s + math.abs(p[i] - q[i])
end
return s
end

return manhattan_distance
``````
``````-- Tests for manhattan_distance.lua
local mdist = require 'manhattan_distance'

local total, pass = 0, 0

local function dec(str, len)
return #str < len
and str .. (('.'):rep(len-#str))
or str:sub(1,len)
end

local function run(message, f)
total = total + 1
local ok, err = pcall(f)
if ok then pass = pass + 1 end
local status = ok and 'PASSED' or 'FAILED'
print(('%02d. %68s: %s'):format(total, dec(message,68), status))
end

-- Fuzzy equality test
local function fuzzyEqual(a, b)
return math.abs(a-b) < 1e-8
end

run('Manhattan distance test', function()
assert(mdist({},{}), 0)
assert(mdist({1,2,3},{4,5,6}), 9)
assert(not pcall(mdist,{1,2,3},{4,5}))
end)

print(('-'):rep(80))
print(('Total : %02d: Pass: %02d - Failed : %02d - Success: %.2f %%')
:format(total, pass, total-pass, (pass*100/total)))
``````