jquery - $.inArray が機能しない

Question

オブジェクトを配列に格納することに関して問題があります。しかし、$.inArray を使用してオブジェクトの存在を確認しようとすると、常に -1 が返されます。私はangularjsを使用しています。

<input name="{{question.number}}"
            ng-click="radioSelected(question.choiceOneWeight, question.number,question.tmiGroup)"
            type="radio" value="{{question.choiceOneWeight}}" />



$scope.radioSelected = function(choice, question, tmiGroup) {
        var answer = {};
        answer.questionNumber = question;
        answer.answerWeight = choice;
        answer.tmiGroup = tmiGroup;

        if($.inArray(answer,userAnswers) < 0){
            userAnswers.push(answer);
        }
    };

私の生成された回答オブジェクトは

{"questionNumber":23,"answerWeight":1,"tmiGroup":"JP"}

ラジオボタンを複数回クリックすると、

userAnswers 配列は次のようになります。

[{"questionNumber":23,"answerWeight":1,"tmiGroup":"JP"},
{"questionNumber":23,"answerWeight":1,"tmiGroup":"JP"},


{"questionNumber":23,"answerWeight":1,"tmiGroup":"JP"},

{"questionNumber":23,"answerWeight":1,"tmiGroup":"JP"},

{"questionNumber":23,"answerWeight":1,"tmiGroup":"JP"},

{"questionNumber":23,"answerWeight":1,"tmiGroup":"JP"},

{"questionNumber":23,"answerWeight":1,"tmiGroup":"JP"},

{"questionNumber":23,"answerWeight":1,"tmiGroup":"JP"},

{"questionNumber":23,"answerWeight":1,"tmiGroup":"JP"},

{"questionNumber":23,"answerWeight":1,"tmiGroup":"JP"},

{"questionNumber":23,"answerWeight":1,"tmiGroup":"JP"},

{"questionNumber":23,"answerWeight":1,"tmiGroup":"JP"},

{"questionNumber":23,"answerWeight":1,"tmiGroup":"JP"},

{"questionNumber":23,"answerWeight":1,"tmiGroup":"JP"},

{"questionNumber":23,"answerWeight":1,"tmiGroup":"JP"},

{"questionNumber":23,"answerWeight":1,"tmiGroup":"JP"},

{"questionNumber":23,"answerWeight":1,"tmiGroup":"JP"}]