Split string into an array of substrings or characters in MongoDB

Question

I need to convert fields like this:

{ 
    \"_id\" : ObjectId(\"576fd6e87d33ed2f37a6d526\"), 
    \"phoneme\" : \"JH OY1 N Z\" 
}

into an a

Answer 1

Suppose that the documents in our collection look like this:

{ "phoneme" : "JH OY1 N Z" }
{ "phoneme" : "foobar" }

In version 3.4+, we can use $split operator to divide the field value into an array of substrings.

To split a string into an array of characters, we need to apply a $substrCP expression to the array of all chars in the string index using the $map operator.

To get the array of index value is all integers from 0 to the string's length minus one which can generate using the $range and the $strLenCP operators.

We use the $addFields pipeline stage to add the new fields to the initial document, but for this to be persistent, we can either create a view or overwrite our collection using the $out aggregation pipeline operator.

[
    {
        "$addFields":{
            "arrayOfPhonemeChar":{
                "$map":{
                    "input":{
                        "$range":[
                            0,
                            {
                                "$strLenCP":"$phoneme"
                            }
                        ]
                    },
                    "in":{
                        "$substrCP":[
                            "$phoneme",
                            "$$this",
                            1
                        ]
                    }
                }
            },
            "phonemeSubstrArray":{
                "$split":[
                    "$phoneme",
                    " "
                ]
            }
        }
    }
]

yields something that look like this:

{
    "phoneme" : "JH OY1 N Z",
    "arrayOfPhonemeChar" : ["J", "H", " ", "O", "Y", "1", " ", "N", " ", "Z"],
    "phonemeSubstrArray" : ["JH", "OY1", "N", "Z"]
},
{
    "phoneme" : "foobar",
    "arrayOfPhonemeChar" : ["f", "o", "o", "b", "a", "r"],
    "phonemeSubstrArray" : ["foobar"]
}