Getting specific object property values from multiple arrays

Question

Say I have a object that looks like this...

values = {
      'student': [{
                     'field': 'prefix', 
                     'description': 'First name'
                  }, 
                  {
                     'field': 'suffix', 
                     'description': 'Last name'
                  }, 
                  {
                     'field': 'student_email',
                     'description': 'Email address'
                  }],
      'classes':  [{
                     'field': 'course_code', 
                     'description': 'Course code'
                  }]

    }

I'm trying to get

['prefix', 'suffix', 'student_email', 'course_code']

So this is what I have:

for (const v in values) {
  v.map((obj, idx) => {
    console.log(obj);
  });
}

And it just returns v.map is not a function. How can I make this work, what am I doing wrong? (written in jsx).

Rick Hitchcock · Accepted Answer · 2016-07-05 22:53:12Z

You're close:

for(const v in values) {
  values[v].map(obj => {
    console.log(obj.field);
    return obj.field;
  });
}

values = {
  'student': [{
    'field': 'prefix',
    'description': 'First name'
  }, {
    'field': 'suffix',
    'description': 'Last name'
  }, {
    'field': 'student_email',
    'description': 'Email address'
  }],
  'classes': [{
    'field': 'course_code',
    'description': 'Course code'
  }]
};

for(const v in values) {
  values[v].map(obj => {
    console.log(obj.field);
    return obj.field;
  });
}

To put them in an array, you could do something like this:

var result = [];

for(const v in values) {
  result = result.concat(values[v].map(obj => {
    return obj.field;
  }));
}

var values = {
  'student': [{
    'field': 'prefix',
    'description': 'First name'
  }, {
    'field': 'suffix',
    'description': 'Last name'
  }, {
    'field': 'student_email',
    'description': 'Email address'
  }],
  'classes': [{
    'field': 'course_code',
    'description': 'Course code'
  }]
};

var result = [];

for(const v in values) {
  result = result.concat(values[v].map(obj => {
    return obj.field;
  }));
}

console.log(result);

Tawnos · Accepted Answer · 2016-07-05 23:01:05Z

The variable values is an object, map() relies on it being an array, as the function is defined on Array.prototype.

Change your variable to this:

values = [
  {
    'student': [{
                 'field': 'prefix', 
                 'description': 'First name'
              }, 
              {
                 'field': 'suffix', 
                 'description': 'Last name'
              }, 
              {
                 'field': 'student_email',
                 'description': 'Email address'
              }]
  },
  {
    'classes':  [{
                 'field': 'course_code', 
                 'description': 'Course code'
              }]
  }
]

Then you can use map on the values array, retrieving what info you need, for example, something like the following should let you map each value and each subvalue:

for (const value in values) {
  value.map((obj) => {
    // should get two calls to the below, one for 'student' and one for 'classes'
    obj.value.map((info) => {
      // should result in 4 calls to log, printing all 'description' values
      console.log(info['description']); 
    }
  });
}

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