Eduction 23.4

# Write a Lua Script for Post-Processing

An Eduction post-processing task runs a Lua script. Eduction passes the matches into an entry function.

There are two available entry functions to use when you process single matches:

- `processmatch`. This function allows you to modify a match, change the score, or discard a non-valid match. You can use this option for most post-processing, such as checksum validation and normalization.
- `finalizematch`. This function allows you to add new matches into the Eduction session. For example, you might use this option to combine existing matches, and return the combined match as a result. This function can also still perform the same changes as `processmatch`.

Your script must define at least one of these functions.

NOTE: If you define both `processmatch` and `finalizematch`, `processmatch` takes precedence.

There are also two equivalent functions for en masse processing, `processmatches` and `finalizematches`. For more information, see Process Matches En Masse.

## Use ProcessMatch

The `processmatch` function must accept an `edkMatch` object (the current match) as its first argument. When you run Eduction through the API, the function can also accept a user parameters map as an optional final argument (see Pass Parameters into the Lua Script).

Eduction passes matches into the script one at a time. The script must return a Boolean value: `true` to keep the match or `false` to discard it.

The following example changes the score for every match to `0.5`:

    function processmatch(edkmatch)
        if edkmatch then
            -- change the score for the match
            edkmatch:setScore(0.5)
        end
        return true
    end

## Use FinalizeMatch

The `finalizematch` entry function must accept an `edkMatch` object (the current match) as its first argument, and a session handle as its second argument. When you run Eduction through the API, the function can also accept a user parameters map as an optional final argument (see Pass Parameters into the Lua Script).

The following example modifies an entity to append the value `Esq.`, and injects the match back into the session.

    function finalizematch(edkmatch, session)
       if edkmatch then
          local text = edkmatch:getOutputText()
          m = LuaEdkMatch:new(edkmatch:getEntityName(), text .. " Esq.", edkmatch:getOffset())
          session:injectMatch(m)
          return true
       end
       return false
    end

After you inject a match, the session takes ownership of it, so you cannot use the created match in any subsequent functions.

NOTE: You cannot perform additional post-processing on injected matches. Eduction skips these matches at post-processing time, to prevent infinite loops.

## Process Matches En Masse

Sometimes, you might prefer to process all the matches together. For example, you might want to increase the scores of matches that appear near other matches. It is easier to do this if you process all the matches at the same time.

To process all the matches at the same time, set the `ProcessEnMasse` parameter to `TRUE` in your Eduction configuration. When `ProcessEnMasse=TRUE`, Eduction passes all the matches it finds into the script together.

Your script for processing matches en masse must define a function either named `processmatches`, or `finalizematches`.

The `processmatches` function must accept a Lua table of `edkEnMasseMatch` objects as its first argument. Each of these objects represents a single match, but you must call the `getMatch` method to obtain an `edkMatch` object. You can then use the `edkMatch` object to manipulate the match. If you want to discard a match, call the method `setOutput` on the relevant `edkEnMasseMatch` object.

The following example demonstrates how to iterate over the elements in the table and discard any match with a score that is less than `0.5`:

    function processmatches(matches)
        -- example that discards matches with score < 0.5
        for k,v in ipairs (matches) do
            local edkmatch = v:getMatch()
            if edkmatch:getScore() < 0.5 then
                v:setOutput(false)
            end
        end
    end

The `finalizematches` function must accept a Lua table of `edkEnMasseMatch` objects as its first argument (the same as for `processmatches`), and a session handle as its second argument.

When you run Eduction through the API, the `processmatches` or `finalizematches` functions can also accept a user parameters map as an optional final argument (see Pass Parameters into the Lua Script).

For information about the objects and methods that you can use in your Lua post-processing scripts, see Eduction Lua Methods Reference.

## Reset a Session

You can define an additional function, `resetprocessor`, which Eduction calls whenever the session resets (for example, when it receives a new input stream, or more text after it has already processed a final input).

You can use this function if your script maintains a global state with details of previous matches. When you reuse the session to process another document or input buffer, you can use `resetprocessor` to reset the state. Eduction passes in the current user parameters (see Pass Parameters into the Lua Script) to the reset hook, if required.

The following simple example shows a script that replaces the normalized text for each match with a count. It resets the count when you reuse your `EdkSession`.

    local count = 0

    function resetprocessor (params)
        count = tonumber(params['startcount']) or 0
    end

    function processmatch (edkmatch)
        if edkmatch then
            count = count + 1
            edkmatch:setOutputText(count)
        end
        return true
    end

## Pass Parameters into the Lua Script

You can pass additional parameters into post-processing tasks that you run through the Eduction API. To add an additional parameter (to all post-processing tasks that run during the session), call the appropriate function:

- `EdkSessionSetUserParamValue` in the C API.
- `ITextExtractionSession::SetUserParameter` in the .NET API.
- `setUserParamValue` in the Java API.

Any parameters that you set using these functions are passed into the `processmatch`, `processmatches`, `finalizematch`, or `finalizematches` function of the Lua script as a table of key-value pairs. For example:

    function processmatch(edkmatch, params)
        for k,v in pairs (params) do
            --print ("Custom parameter ", k, " has value ", v)
        end
        return true
    end

TIP: Some of the Lua post-processing scripts available in the Eduction packages provide optional user parameters. You can review these scripts for the available parameters, and pass them into the task as required. See Example Scripts.

Copyright 2013-2023 Open Text
Version 23.4 | Last updated September 2023

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Product: IDOL Eduction 23.4

Topic Title: Write a Lua Script for Post-Processing