JavaScript - count occurrence of strings

Question

I'm looking to count the occurances of certain strings within JSON - in this instance sensorUUID .

var newDataArray = JSON.stringify(conData);

JSON

[{"blobJson":"x","deviceMfg":10,"eventCode":0,"sensorClass":3,"sensorUUID":"22489710","timeStamp":1500362037.111941,"uID":"22489710_3_10"},{"blobJson":"x","deviceMfg":10,"eventCode":0,"sensorClass":3,"sensorUUID":"22489710","timeStamp":1500362036.109874,"uID":"22489710_3_10"}]

I've tried the following code but it is returning an empty object.

var obj = {};

for (var i = 0, j = newDataArray.length; i < j; i++) {
  if (obj[newDataArray[i].sensorUUID]) {
    obj[newDataArray[i]]++;
  }
}

console.log(obj);

The full JSON file will have multiple sensor ID's within it, I am looking to return the number of unique sensor ID.

eg

22489710 has 10 occurrences

63846683 has 23 occurrences

etc.

Answer 1

the if condition in for loop is correct but you have to initialize count as 1 for the first time you find a particular sensorUUID.

 var newDataArray = [{"blobJson":"x","deviceMfg":10,"eventCode":0,"sensorClass":3,"sensorUUID":"22489710","timeStamp":1500362037.111941,"uID":"22489710_3_10"},{"blobJson":"x","deviceMfg":10,"eventCode":0,"sensorClass":3,"sensorUUID":"22489710","timeStamp":1500362036.109874,"uID":"22489710_3_10"}]; var obj = {}; for (var i = 0, j = newDataArray.length; i < j; i++) { if (obj[newDataArray[i].sensorUUID]) { obj[newDataArray[i].sensorUUID]++; }else{ obj[newDataArray[i].sensorUUID] = 1; } } // obj gives you count for each unique sensorUUID. console.log(obj); //if you want total count of all sensorUUID you can sum all the values in obj. var count = Object.values(obj).reduce((a, b) => a + b, 0); console.log(count); 

Answer 2

You can simply iterate through the json array using array.reduce and count the occurances of sensorUUID and store it inside the new object.

 var json = [{ "blobJson": "x", "deviceMfg": 10, "eventCode": 0, "sensorClass": 3, "sensorUUID": "22489710", "timeStamp": 1500362037.111941, "uID": "22489710_3_10" }, { "blobJson": "x", "deviceMfg": 10, "eventCode": 0, "sensorClass": 3, "sensorUUID": "22489710", "timeStamp": 1500362037.111941, "uID": "22489710_3_10" }, { "blobJson": "x", "deviceMfg": 10, "eventCode": 0, "sensorClass": 3, "sensorUUID": "22489710123", "timeStamp": 1500362036.109874, "uID": "22489710_3_10" }]; let count = json.reduce((newObj, obj) => { if(newObj[obj.sensorUUID]) { newObj[obj.sensorUUID] = newObj[obj.sensorUUID]+1; } else { newObj[obj.sensorUUID] = 1; } return newObj; }, {}); console.log(count); 

Answer 3

you can set a variable count and iterate over the array using Array#forEach and check whether the object has the property sensorUUID using Object#hasOwnProperty if yes, increment the count

 var data = [{"blobJson":"x","deviceMfg":10,"eventCode":0,"sensorClass":3,"sensorUUID":"22489710","timeStamp":1500362037.111941,"uID":"22489710_3_10"},{"blobJson":"x","deviceMfg":10,"eventCode":0,"sensorClass":3,"sensorUUID":"22489710","timeStamp":1500362036.109874,"uID":"22489710_3_10"}]; var count = 0; data.forEach((x)=>{ if(x.hasOwnProperty('sensorUUID')) count++; }); console.log(count); 

Answer 4

https://jsfiddle.net/7jjoches/1/

Using jquery method $.parseJSON you have to convert the JSON string to a JSON object and only then you can work with it.

 var conData = '[{"blobJson":"x","deviceMfg":10,"eventCode":0,"sensorClass":3,"sensorUUID":"22489710","timeStamp":1500362037.111941,"uID":"22489710_3_10"},{"blobJson":"x","deviceMfg":10,"eventCode":0,"sensorClass":3,"sensorUUID":"22489710","timeStamp":1500362036.109874,"uID":"22489710_3_10"}]'; var newDataArray = $.parseJSON(conData); console.dir(newDataArray); var obj = {}; for (var i = 0; i< newDataArray.length; i++) { obj[newDataArray[i].sensorUUID] = obj[newDataArray[i].sensorUUID] ? obj[newDataArray[i].sensorUUID]+1 : 1; } console.log(obj); 

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