如何从对象的数组中挑选数据并将其插入Javascript中的对象的另一个数组中？

Question

I have variable qstore that's has an ans array containing a list of responses. The field named r is used to hold the response data (true or false) and is stored in an array called ans

qstore: {"id":2,
         "qId":2,
         "ans":[{"r":true},
                {"r":true},
                {"r":false},
                {"r":false},
                {"r":false}]}

Another variable qview:

qview: {"problemId":2,
          "questionId":1,
          "answer":null,
          "text":"xx",
          "answers":[{"answerId":1,
                      "response":false},
                     {"answerId":2,
                      "response":false},
                     {"answerId":3,
                      "response":false},
                     {"answerId":4,
                      "response":false},
                     {"answerId":5,
                       "response":false}]}

What I need to do is IF there is an array called ans in qstore (there may not be one) then I need to take the answer responses field r and use that to update the answers response field in the qview object. Note that the qview and qstore if they do have answers will always have the same number of answers.

Can anyone tell me a simple way that I can do this?

Answer 1

What I need to do is IF there is an array called ans in qstore (there may not be one) then I need to take the answer responses field r and use that to update the answers response field in the qview object. Note that the qview and qstore if they do have answers will always have the same number of answers.

// assuming `qstore`, `qview`
var i, j, ans = qstore.ans;
if (ans) { // if qstore has non-falsy ans
    qstore: for (i = 0, j = 0; i < ans.length; ++i) { // loop over ans
        for (; j < qview.answers.length; ++j) { // look in qview
            if (qview.answers[j].answerId === i + 1) { // qview has already
                qview.answers[j].response = ans[i].r;
                continue qstore; // go back to looping ans
            } else if (qview.answers[j].answerId <= i) { // qview needs new
                break; // get out of qview loop
            }
        } // if we reach here then qview didn't have an entry for this item
        qview.answers.splice(j, 0, { // insert new entry
            'answerId': i + 1,
            'response': ans[i].r
        });
    }
}

Answer 2

Just simply loop over the qstore.ans array (if it exists) and set the respective value in qview .

if(qstore.hasOwnProperty('ans')){
    for(var i = 0, len = qstore.ans.length; i < len; i++){
        qview.answers[i].response = qstore.ans[i].r;
    }
}

Answer 3

The most simple solution.

This way it will execute only if you have at less, 1 register on ans array , i see that the solutions above do not verify if the ans array have registers, so i think it is the right one for your case.

Here is the code:

if (qstore.ans != null){
    if (qstore.ans.length > 0){
        for (i=0;i<qstore.ans.length);i++){
            qview.answers[i].response = qstore.ans[i].r;
        }
    }
}

Answer 4

JavaScript has an multiple ways to check if a key exists in an object: in and Object.hasOwnProperty . The difference between the two is that in also returns true if the key is found in the prototype chain of your object.

Now it appears the id's of your response are 1-indexed, but that doesn't matter if we iterate over the index of its position in the array itself:

if ('ans' in qstore) {
    for (var i = 0; i <= qstore.ans.length; i++) {
        qview.answers[[i].response = qstore.ans[i].r
    }
}

There's also a nicer forEach available, if you're not expecting to support IE8 and earlier, or are prepared to insert a "shim":

if ('ans' in qstore) {
    qstore.ans.forEach(function(element, index) {
        element.response = qstore.ans[index].r
    })
}