Node-RED: Lecture 6 – Example 6.2 Counting words in a string using a function Node

Next, let’s write a more complex function node that receives some text in a message payload, then outputs multiple messages containing all individual words and the number of times each word was used.

Listing 6.3 Word count function

1. var outputMsgs = [];
2. var wordMap = {};
4. var sentence = msg.payload.replace(/[.,-\/#!$%\^&\*;:{}=\-_`~()]/g,””);
5. sentence = sentence.replace(/\s{2,}/g,” “);
7. var words = sentence.split(” “);
8. for (var i = 0; i < words.length; i++) {
9.   var lowerCaseWord = words[i].toLowerCase();
10.   if (!wordMap[lowerCaseWord]) {
11.     wordMap[lowerCaseWord] = 1;
12.   } else {
13.     wordMap[lowerCaseWord] = wordMap[lowerCaseWord] + 1;
14.   }
15. }
16. for (var prop in wordMap) {
17.   if( wordMap.hasOwnProperty( prop ) ) {
18.     outputMsgs.push({payload:{word:prop,count:wordMap[prop]}});
19.   }
20. }
21. return [outputMsgs];

In Listing 6.3, the list of output messages and an object to hold the word counts (Lines 1 and 2) is declared. In lines 4 and 5 the payload is ‘cleaned’, removing punctuation and extra spaces using regular expressions. Regular expressions are a very useful tool for text processing; you can learn more about regular expressions by looking at the Mozilla Developers pages for JavaScript (here).  Line 7 splits the text into multiple words, then iterates through the words, creating a mapping of the lowercase version of each word to word count called wordMap in Lines 8-15.  Lines 16 to 18 split the wordMap into multiple messages in the outputMsgs array^[1].   Finally, in line 21, an array of this array of messages is returned, sending them all to the first output port one at a time^[2].

Let’s wire this up and see it run with some example text.  First, create a function node, and copy in the code above. Call it word count. Then add an inject node and add the following text:

Figure 6.7 Inject node to test word count function node.

Add a debug node and wire up the flow as follows:

Figure 6.8 Test flow for word count function node.

When you click on the inject node, you should see the list of word counts in the debug pane:

Figure 6.9 Debug output from word count function node.

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