Converting a string to an array in Lua

Question

Why does this syntax work:

if ({A=1,B=1,C=1})["A"]  then print("hello") end

while this does not:

local m = {string.sub(string.gsub("A,B,C,", ",", "=1,"),1,-2)}

if (m)["A"]  then print("hello") end

???

I think it's because a string is not an array, but how can I convert a string ("a,b,c") to an array ({a=1,b=1,c=1})?

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Community · Accepted Answer · 2020-06-20 09:12:55Z

5

This line

local m = {string.sub(string.gsub("A,B,C,", ",", "=1,"),1,-2)}

is equivalent to this

local v = string.sub(string.gsub("A,B,C,", ",", "=1,"),1,-2)
local m = {v}

which, I hope you agree, would clearly not have the behavior of assigning multiple values in the m table.

To "parse" simple a=1,b=1,c=1 type strings into a table the second example of string.gmatch from the manual is helpful:

The next example collects all pairs key=value from the given string into a table:
t = {}
s = "from=world, to=Lua"
for k, v in string.gmatch(s, "(%w+)=(%w+)") do
  t[k] = v
end

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Feb 25, 2015 at 23:50

Etan Reisner

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2 Comments

Colonel Thirty Two Over a year ago

Note: the two samples are not equivalent in general; the second one truncates the result of string.sub to one value, while the first sample will store all return values in the array.

Etan Reisner Over a year ago

@ColonelThirtyTwo While true string.sub only ever returns one value.

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