In Lua, I want to select the parts of the array. The below example selects from the second elements
a = { 1, 2, 3}
print(a)
b = {}
for i = 2, table.getn(a) do
table.insert(b, a[i])
end
print(b)
In python a[1:] works. Does Lua have the similar syntax?
Lua does not have similar syntax. However, you can define your own function to easily wrap this logic up.
local function slice (tbl, s, e)
local pos, new = 1, {}
for i = s, e do
new[pos] = tbl[i]
pos = pos + 1
end
return new
end
local foo = { 1, 2, 3, 4, 5 }
local bar = slice(foo, 2, 4)
for index, value in ipairs(bar) do
print (index, value)
end
Note that this is a shallow copy of the elements in foo to bar.
Alternatively, in Lua 5.2 you could use table.pack and table.unpack.
local foo = { 1, 2, 3, 4, 5 }
local bar = table.pack(table.unpack(foo, 2, 4))
Although the manual has this to say:
table.pack (···)
Returns a new table with all parameters stored into keys 1, 2, etc. and with a field "n" with the total number of parameters. Note that the resulting table may not be a sequence.
While Lua 5.3 has table.move:
local foo = { 1, 2, 3, 4, 5 }
local bar = table.move(foo, 2, 4, 1, {})
And finally, most would probably opt to define some kind of OOP abstraction over this.
local list = {}
list.__index = list
function list.new (o)
return setmetatable(o or {}, list)
end
function list:append (v)
self[#self + 1] = v
end
function list:slice (i, j)
local ls = list.new()
for i = i or 1, j or #self do
ls:append(self[i])
end
return ls
end
local foo = list.new { 1, 2, 3, 4, 5 }
local bar = foo:slice(2, 4)
table.getn(t)it I'd bad practice, please use#t