Csv file to a Lua table and access the lines as new table or function()

Question

Currently my code have simple tables containing the data needed for each object like this:

infantry = {class = "army", type = "human", power = 2} 

cavalry = {class = "panzer", type = "motorized", power = 12} 

battleship = {class = "navy", type = "motorized", power = 256}

I use the tables names as identifiers in various functions to have their values processed one by one as a function that is simply called to have access to the values.

Now I want to have this data stored in a spreadsheet (csv file) instead that looks something like this:

Name    class  type     power 

Infantry   army   human        2 

Cavalry    panzer motorized   12 

Battleship navy   motorized  256  

The spreadsheet will not have more than 50 lines and I want to be able to increase columns in the future.

Tried a couple approaches from similar situation I found here but due to lacking skills I failed to access any values from the nested table. I think this is because I don't fully understand how the tables structure are after reading each line from the csv file to the table and therefore fail to print any values at all.

If there is a way to get the name,class,type,power from the table and use that line just as my old simple tables, I would appreciate having a educational example presented. Another approach could be to declare new tables from the csv that behaves exactly like my old simple tables, line by line from the csv file. I don't know if this is doable.

Using Lua 5.1

Answer 1

You can read the csv file in as a string . i will use a multi line string here to represent the csv.

gmatch with pattern [^\n]+ will return each row of the csv. gmatch with pattern [^,]+ will return the value of each column from our given row.

if more rows or columns are added or if the columns are moved around we will still reliably convert then information as long as the first row has the header information.

The only column that can not move is the first one the Name column if that is moved it will change the key used to store the row in to the table.

Using gmatch and 2 patterns, [^,]+ and [^\n]+, you can separate the string into each row and column of the csv. Comments in the following code:

local csv = [[
Name,class,type,power
Infantry,army,human,2
Cavalry,panzer,motorized,12
Battleship,navy,motorized,256
]]

local items = {}                      -- Store our values here
local headers = {}                    -- 
local first = true
for line in csv:gmatch("[^\n]+") do
  if first then                       -- this is to handle the first line and capture our headers.
    local count = 1
    for header in line:gmatch("[^,]+") do 
      headers[count] = header
      count = count + 1
    end
    first = false                     -- set first to false to switch off the header block
  else
    local name
    local i = 2                       -- We start at 2 because we wont be increment for the header
    for field in line:gmatch("[^,]+") do
      name = name or field            -- check if we know the name of our row
      if items[name] then             -- if the name is already in the items table then this is a field
        items[name][headers[i]] = field -- assign our value at the header in the table with the given name.
        i = i + 1
      else                            -- if the name is not in the table we create a new index for it
        items[name] = {}
      end
    end
  end
end

Here is how you can load a csv using the I/O library:

-- Example of how to load the csv. 
path = "some\\path\\to\\file.csv"
local f = assert(io.open(path))
local csv = f:read("*all")
f:close()

Alternative you can use io.lines(path) which would take the place of csv:gmatch("[^\n]+") in the for loop sections as well.

Here is an example of using the resulting table:

-- print table out
print("items = {")
for name, item in pairs(items) do
  print("    " .. name .. " = { ")
  for field, value in pairs(item) do
    print("        " .. field .. " = ".. value .. ",")
  end
  print("    },")
end
print("}")

The output:

items = {
    Infantry = { 
        type = human,
        class = army,
        power = 2,
    },
    Battleship = { 
        type = motorized,
        class = navy,
        power = 256,
    },
    Cavalry = { 
        type = motorized,
        class = panzer,
        power = 12,
    },
}