Setting an empty array index

Question

i have an array that holds student answers for given questions.

if a student gives an answer, it gets inserted into the array at the current index like answers[questionindex] = answer

later, i can read the array and map the entries to the given question-array

this case:

[
"answer",
undefined, // student has not given answer
"answer2",
]

works. (looping over the array, simply outputting "no answer given" if (answers[questionindex] === undefined)

but it doesn't work when the LAST answers were undefined (1 or more) they just don't exist (of course).

how can i set those fields to undefined (like, after a timer reaches zero), to show that there was no answer given?

right now, the average-calculation shows 100% correct for 3 given (correctly), then 2 not given at all

code

var testResults = {

    addRoom: function(Id, teacher) {  // room pseudoconstructor

        this[Id] = {


            created: moment(),

            runningProblem: false,

            time: 0, // holds the countdown for the current problem

            getTime: function() { // returns the countdown-counter
                return this.time;
            },

            Id: Id,

            teacher: teacher,

            getCurrentSolution: function() {
                return math.eval(this.testProblems[this.getCurrentProblemIndex()].problem);
            },

            getTimeTaken: function() {
                return this.getCurrentProblemTimeLimit() - this.time;
            },

            getCurrentProblemTimeLimit: function() {
                return this.testProblems[this.getCurrentProblemIndex()].timeLimit;
            },

            getCurrentProblemIndex: function() {
                return this.testProblems.length - 1;
            },

            addTestProblem: function(problem, timeLimit) {
                var solution = math.eval(problem);

                this.testProblems.push({problem: problem, timeLimit: timeLimit, solution: solution});
                console.dir(this.testProblems);
            },

            testProblems: [],

            updatePercentages: function(name) {

                function round(num) {
                    return +(Math.round(num + "e+2")  + "e-2");
                }

                console.log('updating percentages');
                console.log('answers length ' + this.students[name].givenAnswers.length);
                var timeSum = 0;
                for(var i = 0; i < this.students[name].givenAnswers.length; i++ ) {
                    timeSum += this.students[name].givenAnswers[i].takenTime;
                }
                var timeAvg = timeSum / this.students[name].givenAnswers.length;

                console.log('timeAvg for ' + name + ' ' + timeAvg);
                this.students[name].avgTime = round(timeAvg);

                var correctSum = 0;
                for(var j = 0; j < this.students[name].givenAnswers.length; j++ ) {
                    if (this.students[name].givenAnswers[j].correct) {
                        correctSum++;
                    }
                }
                var correctAvg = correctSum / this.students[name].givenAnswers.length;


                console.log('correctAvg for ' + name + ' ' + correctAvg);
                this.students[name].avgCorrect = round(correctAvg) * 100;
            },

            addGivenStudentAnswer: function(name, answer, takenTime, index) {

                console.log('adding answer ' + name + ' ' +answer+ ' ' + takenTime);

                var correct = this.getCurrentSolution() == answer;

                if (typeof this.students[name].givenAnswers[index] === 'undefined') {
                    this.students[name].givenAnswers[index] = ({
                        answer: answer,
                        takenTime: takenTime,
                        correct: correct
                    });
                    this.updatePercentages(name);
                    //console.dir(this.students[name].givenAnswers);
                    return true;

                } else {
                    console.log('attempt at double answer. not saved');
                    return false;
                }
            },

            addStudent: function(name) {
                if (!(this.students[name])) {
                    this.students[name] = {
                        studentName : name,
                        avgTime: 0,
                        avgCorrect: 0,
                        givenAnswers: []
                    }
                }
                console.dir(this);
            },
            students: {}
        };

        console.dir(this);

    },

    deleteRoom: function(Id) {
        delete this[Id];
        console.log('room deleted from testResults');
    }
};

// after test

var name = socket.userName;
        var room = socket.room;
        var created = testResults[room].created;
        var students = testResults[room].students;
        var problems = testResults[room].testProblems;

var test = new tests({
                roomId      : room,
                created     : created,
                teacher     : name,
                students    : students,
                problems    : problems
            });

            test.save(function(err, result) {
                if (err) {console.log(err);}
                else {
                    console.log('test saved to DB');
                    socket.emit('testSaved');
                    // delete from roomList
                    testRooms.deleteRoom(room, name);
                    // delete from resultObject
                    testResults.deleteRoom(room);
                    // answer
                    io.in(room).emit('room Closed');
                }
            });

route for reading a test from DB afterwars

router.get('/showtests/:roomId', function(req, res) {
    if (req.user && req.user.role === 'teacher') {
        tests.findOne({roomId: req.params.roomId}, {}, function(err, result) {
            if (err) {console.log(err);}
            res.render('showSingleTest', {user: req.user, testData: JSON.parse(JSON.stringify(result))});
        })
    } else {
        res.render('customerror', { title: "Error", errMsg1: "error.error", errMsg2: "error.notLoggedIn" });
    }
});

aaaaaand the jade

h2(data-i18n="markup.studentsAnswers")
each student in testData.students
    .testViewSingleStudentAnswers.col-md-6
        h3 #{student.studentName}

        ol.answers
            each answer in student.givenAnswers
                if (answer)
                    if (answer.correct == true)
                        li.correct
                            span #{answer.answer}
                            | &nbsp;&nbsp;&nbsp;
                            span.floatRight (#{answer.takenTime}s)
                    else
                        li.wrong
                            span #{answer.answer}
                            | &nbsp;&nbsp;&nbsp;
                            span.floatRight (#{answer.takenTime}s)
                else
                    li.noAnswer(data-i18n="markup.noAnswerGiven")
        .testTotals
            | #{student.avgCorrect}
            span(data-i18n="markup.percentCorrect")
            | ,&nbsp;
            | #{student.avgTime}
            span(data-i18n="markup.avgTime")

Don't you know the total amount of questions? Couldn't you simply fill out answers initially with all NULL values? — h2ooooooo
– h2ooooooo, Commented Feb 4, 2016 at 15:00
no, it's totally dynamic. the teacher can add any number of questions, one at a atime — user3787706
– user3787706, Commented Feb 4, 2016 at 15:01
You need to provide more code about everything you're doing with these answers and questions. You know on a given page how many questions there are beforehand, correct? There's just too many "architecture" questions to give you a proper answer. Most likely there are several things you're doing that can be done better. — krillgar
– krillgar, Commented Feb 4, 2016 at 15:04

Daniel Mizerski · Accepted Answer · 2016-02-04 15:04:06Z

2

You can do like so:

function push_answer(answer){
answer = answer || "undefined"
array_of_answers.push(answer)
}

Now, the value is not undefined, but it's defined by the literal. You can replace it with some unicode character in case some answer can be "undefined".

Have a nice day!

answered Feb 4, 2016 at 15:04

Daniel Mizerski

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Comments

Redmega · Accepted Answer · 2016-02-04 15:09:58Z

0

Seems to be working without issue for me.

HTML:

<div id="content">

</div>

JS:

var answers = ["answer1","answer2",undefined,"answer3",undefined];

for(i=0;i<answers.length;i++) {
  if(!answers[i]){
    answers[i]="no answer";
  }
}
document.getElementById('content').innerHTML = answers;

jsFiddle

answered Feb 4, 2016 at 15:09

Redmega

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1 Comment

user3787706 Over a year ago

would this work? pastebin.com/skbUpKFv webstorm shows an error that "testProblems" is unresolved, even though it definitely exists. how can i access it? (all previous uses seem to work, only the innermost call gets underlined)

Diego Fernando Villarroel Diaz · Accepted Answer · 2016-02-04 15:10:47Z

0

My personal recomendation: "Never leave things to chance"

if the student doesn't choose an answer, you should fill that blank space with a '', because undefined is really annoying to handle, so in order to fill the gaps:

This will check if answer is "undefined" and fill the gap with a '' (blank), then, when you check that answer, is going to be more simple to evaluate...

if(answer)
   answers[questionindex] = answer;
else
   answers[questionindex] = '';

answered Feb 4, 2016 at 15:10

Diego Fernando Villarroel Diaz

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