Tables as Data Structures

Numeric Lookup

Array-style Lua tables use numeric indexes starting at 1.

one based index Read a value by putting the numeric position inside brackets.

Numeric Lookup

index
numeric_lookup.lua
Replay: real traced execution (multi-file project)
local index = 2
local color = ({"red", "blue", "green"})[index]

print("index=" .. index)
print("color=" .. color)

local index = 1
local color = ({"red", "blue", "green"})[index]

print("index=" .. index)
print("color=" .. color)

local index = 3
local color = ({"red", "blue", "green"})[index]

print("index=" .. index)
print("color=" .. color)

  1. index ← 2, color ← blue

    1local index→ 2 = 2 --@index=1, 32local color→ blue = ({"red", "blue", "green"})[index]blue34print("index=" .. index2)5print("color=" .. colorblue)
    outputindex=2
color=blue

  1. index ← 1, color ← red

    1local index→ 1 = 12local color→ red = ({"red", "blue", "green"})[index]red34print("index=" .. index1)5print("color=" .. colorred)
    outputindex=1
color=red

  1. index ← 3, color ← green

    1local index→ 3 = 32local color→ green = ({"red", "blue", "green"})[index]green34print("index=" .. index3)5print("color=" .. colorgreen)
    outputindex=3
color=green

Pick by Position

  1. The table holds red, blue, and green.
  2. Lua positions start at 1.
  3. index is 2.
  4. The lookup returns blue. | Index | Value | Selected? | | --- | --- | --- | | 1 | red | no | | 2 | blue | yes | | 3 | green | no |

Exercise: numeric_lookup.lua

Pick a color from a table by numeric index and print the index and color