node-red/nodes/core/logic/17-split.html

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<script type="text/x-red" data-help-name="split">
    <p>Splits a message into a sequence of messages.</p>

    <h3>Inputs</h3>
    <dl class="message-properties">
        <dt>payload<span class="property-type">object | string | array | buffer</span></dt>
        <dd>The behaviour of the node is determined by the type of <code>msg.payload</code>:
            <ul>
                <li><b>string</b>/<b>buffer</b> - the message is split using the specified character (default: <code>\n</code>), buffer sequence or into fixed lengths.</li>
                <li><b>array</b> - the message is split into either individual array elements, or arrays of a fixed-length.</li>
                <li><b>object</b> - a message is sent for each key/value pair of the object.</li>
            </ul>
        </dd>
    </dl>
    <h3>Outputs</h3>
    <dl class="message-properties">
        <dt>parts<span class="property-type">object</span></dt>
        <dd>This property contains information about how the message was split from
        the original message. If passed to the <b>join</b> node, the sequence can be
        reassembled into a single message. The property has the following properties:
        <ul>
            <li><code>id</code> - an identifier for the group of messages</li>
            <li><code>index</code> - the position within the group</li>
            <li><code>count</code> - if known, the total number of messages in the group. See 'streaming mode' below.</li>
            <li><code>type</code> - the type of message - string/array/object/buffer</li>
            <li><code>ch</code> - for a string or buffer, the data used to the split the message as either the string or an array of bytes</li>
            <li><code>key</code> - for an object, the key of the property this message was created from. The node can be configured to also copy this value to another message properties, such as <code>msg.topic</code>.</li>
            <li><code>len</code> - the length of each message when split using a fixed length value</li>
        </ul>
        </dd>
    </dl>
    <h3>Details</h3>
    <p>This node makes it easy to create a flow that performs common actions across
    a sequence of messages before, using the <b>join</b> node, recombining the
    sequence into a single message.</p>
    <p>It uses the <code>msg.parts</code> property to track the individual parts
    of a sequence.</p>
    <h4>Streaming mode</h4>
    <p>The node can also be used to reflow a stream of messages. For example, a
    serial device that sends newline-terminated commands may deliver a single message
    with a partial command at its end. In 'streaming mode', this node will split
    a message and send each complete segment. If there is a partial segment at the end,
    the node will hold on to it and prepend it to the next message that is received.
    </p>
    <p>When operating in this mode, the node will not set the <code>msg.parts.count</code>
    property as it does not know how many messages to expect in the stream. This
    means it cannot be used with the <b>join</b> node in its automatic mode</p>
</script>

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<script type="text/x-red" data-help-name="join">
    <p>Joins sequences of messages into a single message.</p>
    <p>There are three modes available:</p>
    <dl>
        <dt>automatic</dt>
        <dd>When paired with the <b>split</b> node, it will automatically join the messages to reverse the split that was performed.</dd>
        <dt>manual</dt>
        <dd>Join sequences of messages in a variety of ways.</dd>
        <dt>reduce sequence</dt>
        <dd>Apply an expression against all messages in a sequence to reduce it to a single message.</dd>
    </dl>
    <h3>Inputs</h3>
    <dl class="message-properties">
        <dt class="optional">parts<span class="property-type">object</span></dt>
        <dd>To automatically join a sequence of messages, they should all have
        this property set. The <b>split</b> node generates this property but it
        can be manually created. It has the following properties:
        <ul>
            <li><code>id</code> - an identifier for the group of messages</li>
            <li><code>index</code> - the position within the group</li>
            <li><code>count</code> - the total number of messages in the group</li>
            <li><code>type</code> - the type of message - string/array/object/buffer</li>
            <li><code>ch</code> - for a string or buffer, the data used to the split the message as either the string or an array of bytes</li>
            <li><code>key</code> - for an object, the key of the property this message was created from</li>
            <li><code>len</code> - the length of each message when split using a fixed length value</li>
        </ul>
        </dd>
        <dt class="optional">complete</dt>
        <dd>If set, the node will send its output message in its current state.</dd>
    </dl>
    <h3>Details</h3>

    <h4>Automatic mode</h4>
    <p>Automatic mode uses the <code>parts</code> property of incoming messages to
       determine how the sequence should be joined. This allows it to automatically
       reverse the action of a <b>split</b> node.

    <h4>Manual mode</h4>
    <p>When configured to join in manual mode, the node is able to join sequences
     of messages into a number of different results:</p>
    <ul>
        <li>a <b>string</b> or <b>buffer</b> - created by joining the selected property of each message with the specified join characters or buffer.</li>
        <li>an <b>array</b> - created by adding each selected property, or entire message, to the output array.</li>
        <li>a <b>key/value object</b> - created by using a property of each message to determine the key under which
        the required value is stored.</li>
        <li>a <b>merged object</b> - created by merging the property of each message under a single object.</li>
    </ul>
    <p>The other properties of the output message are taken from the last message received before the result is sent.</p>
    <p>A <i>count</i> can be set for how many messages should be received before generating the output message.
    For object outputs, once this count has been reached, the node can be configured to send a message for each subsequent message
    received.</p>
    <p>A <i>timeout</i> can be set to trigger sending the new message using whatever has been received so far.</p>
    <p>If a message is received with the <b>msg.complete</b> property set, the output message is sent.</p>

    <h4>Reduce Sequence mode</h4>
    <p>When configured to join in reduce mode, an expression is applied to each
       message in a sequence and the result accumulated to produce a single message.</p>

    <dl class="message-properties">
        <dt>Initial value</dt>
        <dd>The initial value of the accumulated value (<code>$A</code>).</dd>
        <dt>Reduce expression</dt>
        <dd>A JSONata expression that is called for each message in the sequence.
            The result is passed to the next call of the expression as the accumulated value.
            In the expression, the following special variables can be used:
            <ul>
                <li><code>$A</code>: the accumulated value, </li>
                <li><code>$I</code>: index of the message in the sequence, </li>
                <li><code>$N</code>: number of messages in the sequence.</li>
            </ul>
        </dd>
        <dt>Fix-up expression</dt>
        <dd>An optional JSONata expression that is applied after the reduce expression
            has been applied to all messages in the sequence.
            In the expression, following special variables can be used:
            <ul>
                <li><code>$A</code>: the accumulated value, </li>
                <li><code>$N</code>: number of messages in the sequence.</li>
            </ul>
        </dd>
        <p>By default, the reduce expression is applied in order, from the first
           to the last message of the sequence. It can optionally be applied in
           reverse order.</p>
    </dl>
    <p><b>Example:</b> the following settings, given a sequence of numeric values,
       calculates the average value:
        <ul>
            <li><b>Reduce expression</b>: <code>$A+payload</code></li>
            <li><b>Initial value</b>: <code>0</code></li>
            <li><b>Fix-up expression</b>: <code>$A/$N</code></li>
        </ul>
    </p>
    <h4>Storing messages</h4>
    <p>This node will buffer messages internally in order to work across sequences. The
       runtime setting <code>nodeMessageBufferMaxLength</code> can be used to limit how many messages nodes
       will buffer.</p>
</script>

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