CODEWITHSUNDEEP
lualua-table
Glupschi
Glupschi

Reputation: 215

save strings in lua table

Does someone know a solution to save the key and the values to an table? My idea does not work because the length of the table is 0 and it should be 3.

local newstr = "3 = Hello, 67 = Hi, 2 = Bye"

a = {}
for k,v in newstr:gmatch "(%d+)%s*=%s*(%a+)" do 
    --print(k,v)
    a[k] = v
end

print(#a)

Upvotes: 3

Views: 460

Answers (2)

Piglet
Piglet

Reputation: 28940

The output is correct.

run for k,v in pairs(a) do print(k,v) end to check the contents of your table.

The problem is the length operator which by default cannot be used to get the number of elements of any table but a sequence.

Please refer to the Lua manual: https://www.lua.org/manual/5.4/manual.html#3.4.7

When t is a sequence, #t returns its only border, which corresponds to the intuitive notion of the length of the sequence. When t is not a sequence, #t can return any of its borders. (The exact one depends on details of the internal representation of the table, which in turn can depend on how the table was populated and the memory addresses of its non-numeric keys.)

Only use the length operator if you know t is a sequence. That's a Lua table with integer indexes 1,..n without any gap.

You don't have a sequence as you're using non-numeric keys only. That's why #a is 0

The only safe way to get the number of elements of any table is to count them.

local count = 0
for i,v in pairs(a) do
  count = count + 1
end

Upvotes: 4

koyaanisqatsi
koyaanisqatsi

Reputation: 2793

You can put @Piglet' code in the metatable of a as method __len that is used for table key counting with length operator #.

local newstr = "3 = Hello, 67 = Hi, 2 = Bye"

local a = setmetatable({},{__len = function(tab)
local count = 0
for i, v in pairs(tab) do
 count = count + 1
end
return count
end})

for k,v in newstr:gmatch "(%d+)%s*=%s*(%a+)" do 
    --print(k,v)
    a[k] = v
end

print(#a) -- puts out: 3

The output of #a with method __len even is correct if the table holds only a sequence.

You can check this online in the Lua Sandbox...
Lua Online CGI Sandbox ...with copy and paste.
Like i do.

Upvotes: 1

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