Include empty matches when using string.gmatch to split a string in lua 5.1

Question

I have a comma seperated input string that needs to support empty entries. So a string like a,b,c,,d should result in a table with 5 entries, where the 4'th is an empty value.

A simplified example

str="a,b,c,,d"
count=0

for v in string.gmatch(str, '([^,]*)') do
    count = count + 1
end

print(count)

This code outputs

9

in Lua 5.1, although there are only 5 entries.

I can change the * in the regex to + - then it reports the 4 entries a,b,c,d but not the empty one. It seems that this behaviour has been fixed in Lua 5.2, because the code above works fine in lua 5.2, but I'm forced to find a solution for lua 5.1

My current implementation

function getValues(inputString)
  local result = {}

  for v in string.gmatch(inputString, '([^,]*)') do
    table.insert(result, v)
  end

  return result
end

Any suggestions about how to fix?

simple workaround: replace the empty positions with a space or "novalue" or whatever suits your needs. — Piglet
– Piglet, Commented Apr 6, 2020 at 7:37

Wiktor Stribiżew · Accepted Answer · 2020-04-06 09:50:31Z

3

You may append a comma to the text and grab all values using a ([^,]*), pattern:

function getValues(inputString)
  local result = {}

  for v in string.gmatch(inputString..",", '([^,]*),') do
    table.insert(result, v)
  end

  return result
end

The output:

a
b
c

d

answered Apr 6, 2020 at 9:50

Wiktor Stribiżew

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1 Comment

Wiktor Stribiżew Over a year ago

@lhf Negated character classes usually perform better.

DarkWiiPlayer · Accepted Answer · 2020-04-06 08:01:45Z

0

local str="a,b,c,,d"
local count=1
for value in string.gmatch(str, ',') do
    count = count + 1
end
print(count)

And if you want to get the values, you could do something like


local function values(str, previous)
    previous = previous or 1
    if previous <= #str then
        local comma = str:find(",", previous) or #str+1
        return str:sub(previous, comma-1), values(str, comma+1)
    end
end

edited Apr 6, 2020 at 8:01

answered Apr 6, 2020 at 7:52

DarkWiiPlayer

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2 Comments

Daniel Over a year ago

Sorry, it wasn't clear in my question that I need the values. I have updated the question accordingly. Would you mind providing an example of how to use this values function?

DarkWiiPlayer Over a year ago

You can just do v = {values("a,b,c,,d")} to get a table with all the values :D

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