Saving multiple data for a user JSON array

For a site I’m working on, a user has the option to input exercise data and it is saved to a JSON file in an array:

{
    "Email": "[e-mail]",
    "ExerciseType": "Running",
    "DistanceTravelled": "35",
},

But what I want it to do is to be able to save it in a multidimensional array so multiple records can be put in for one user.

Example:

{
    "[e-mail]"
                      {
                        "ExerciseType": "Running",
                        "DistanceTravelled": "35",
                      }
}

That way multiple records for the user are saved under one primary object to make it easier to access later. However I’ve never used multi-dimensional arrays before so I can’t figure out how to modify my code to get this to work.

        // Save data
        $file = ('data.json');
        $arr = array();

        $new_userstats = array (
        'Email' => $email,
        'ExerciseType' => $exerciseType,
        'DistanceTravelled' => $distance
        );

        $jsondata = file_get_contents($file);

        $arr_data = json_decode($jsondata, true);

        array_push($arr_data, $new_userstats);

        $jsondata = json_encode($arr_data, JSON_PRETTY_PRINT);

        file_put_contents($file,$jsondata);

Answer

If Email is the attribute to uniquely identify a user. It would be great to keep this as key of our array to easily find and add a new data to existing file.

Now the format we would be storing in file looks like

{
    "[e-mail]" : [
        {
            "ExerciseType": "Running",
            "DistanceTravelled": "35",
        },
        {
            "ExerciseType": "Jogging",
            "DistanceTravelled": "13",
        },
    ],
    "[e-mail]" : [
        {
            "ExerciseType": "Running",
            "DistanceTravelled": "11",
        },
    ]
}

Now how to add new data to this file would be in following way.

// Fetch existing data
$strFile = 'data.json';
$arrExistingData = json_decode(file_get_contents($strFile), true);

// Add new data to existing data, new data would contain and object in following way
$arrNewData     =   [
    'ExerciseType' => $exerciseType,
    'DistanceTravelled' => $distance
];

$arrExistingData[$email][]  = $arrNewData;

// Save data back to file, avoid JSON_PRETTY_PRINT to reduce the file size.
file_put_contents($strFile, json_encode($arrExistingData));