CODEWITHSUNDEEP
parsinglualua-table
user2609216
user2609216

Reputation: 35

Parsing large .txt files in Lua without tables

I'm reasonably new to Lua although I have used other languages which are similar. So far I've spent 8 hours to no avail trying to parse a large text file.

The file in question looks something like this: (but thousands of lines long)

A|KLAX|LOS ANGELES INTERNATIONAL|33942522|-118407161|125

I've got the user to enter the KLAX variable, but my goal is to get out this part of the line in question WITHOUT using tables: 33942522|-118407161

E.g.

APTDEP_DATA = 33942522|-118407161

Or even get a whole line out of the .txt file as a string?

E.g.

APTDEP_DATA = A|KLAX|LOS ANGELES INTERNATIONAL|33942522|-118407161|125

Thanks a heap in advance. After 8 hours, it would be great to know whether what I'm trying to do is even possible. (Every tutorial I see is parsing data into tables)

I've tried a lot of things to this effect:

THE NZAA is also a code I was trying to find. So don't get confused with KLAX thing. I was just trying to get a result.

(I couldn't get the code to show properly, sorry about the link)

Upvotes: 0

Views: 561

Answers (2)

greatwolf
greatwolf

Reputation: 20858

From looking at your example snippet, the problem is coming from your usage of:

AP_LAT = string.match(file, "A|NZAA")

Pattern matching is performed on a string value, not a file handle. More appropriate would be:

AP_LAT = string.match(line, "A|NZAA")

The following processes your input file a line at a time and also parses it to its respective fields:

file = assert(io.open("Airports.txt", "r"))

for line in file:lines() do
  local fields = { line:match "(%w+)|(%w+)|([%w ]+)|([%d-]+)|([%d-]+)|([%d-]+)" }
  -- do something useful with it
  print(fields[4], fields[5])  -- the 2 numeric fields you're interested in
end

file:close()

If you're adamant about no tables, you can just punt the matches into variables like this:

local first, second, third, etc = line:match "(%w+)|(%w+)|([%w ]+)|([%d-]+)|([%d-]+)|([%d-]+)"

Note: Feel free to modify/refine the pattern to suit your needs. This is just an example to illustrate the idea.

Upvotes: 4

Yu Hao
Yu Hao

Reputation: 122483

To read lines from a file, use io.lines:

for line in io.lines(filename) do 
    --do some processing
end

To get specific part from the line, use pattern matching. I'm not sure what you are trying to get from the question.

Upvotes: 0

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