javascript - How to create an array of all first letters from object properties in another multidimentional array? - Stack Overf

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I have an array with objects, and each object containing a property called name.

Now i want to have a second array containing the first letter of each name property from the first array. This first letter should be saved in a property called header if it doesn't exist yet.

I only want to have a letter to appear once, as this script is intended to be used for a list of alphabetic headers, each containing a list of names starting with the same letter.

I have created a function that uses the build-in JavaScript "filter" method, which is supposed to check if a value with this first letter already exists. But for some reason it doesn't work. The filter always returns an empty array, no matter what letter i provide.

I have been trying to figure out why my script is not working with no success. I greatly appreciate any help with this!

var fruit = [{title:"Apple"},{title:"Avocado"},{title:"Banana"},{title:"Cucumber"}];
var sections = [];
function createAlphabetSections(array) {
        for(var i = 0; i < array.length; i++){
            var firstLetter = array[i].title.charAt(0).toUpperCase();
            var section = sections.filter(function (section) { return section.header === firstLetter;});
            if(sections.length === 0){
                sections.push([{header: firstLetter}]);  
            } else if (section.length > 0){
                sections.push([{header: firstLetter}]);
            }
        }
}
createAlphabetSections(fruit);

I have an array with objects, and each object containing a property called name.

Now i want to have a second array containing the first letter of each name property from the first array. This first letter should be saved in a property called header if it doesn't exist yet.

I only want to have a letter to appear once, as this script is intended to be used for a list of alphabetic headers, each containing a list of names starting with the same letter.

I have created a function that uses the build-in JavaScript "filter" method, which is supposed to check if a value with this first letter already exists. But for some reason it doesn't work. The filter always returns an empty array, no matter what letter i provide.

I have been trying to figure out why my script is not working with no success. I greatly appreciate any help with this!

var fruit = [{title:"Apple"},{title:"Avocado"},{title:"Banana"},{title:"Cucumber"}];
var sections = [];
function createAlphabetSections(array) {
        for(var i = 0; i < array.length; i++){
            var firstLetter = array[i].title.charAt(0).toUpperCase();
            var section = sections.filter(function (section) { return section.header === firstLetter;});
            if(sections.length === 0){
                sections.push([{header: firstLetter}]);  
            } else if (section.length > 0){
                sections.push([{header: firstLetter}]);
            }
        }
}
createAlphabetSections(fruit);

• javascript
• arrays
• object
• filter

Share Improve this question Follow asked Nov 5, 2015 at 14:40 kleinermannkleinermann 5522 silver badges1010 bronze badges 2

• Please provide an example of expected function output. – halfzebra Commented Nov 5, 2015 at 14:42
• The function should return an array of objects. Each object should have a property called header, which has the first letter of each title property from the first array assigned to it. Duplicates should be removed: [Object { headerTitle="A"}, Object { headerTitle="B"}, Object { headerTitle="C"}] – kleinermann Commented Nov 8, 2015 at 13:43

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2 Answers 2

Sorted by: Reset to default 7

First make use map to build a new array from the current array. Then filter out any duplicates.

var sections = fruit.map(function (item) {
    // Return the first letter of the title property
    return item.title.substring(0, 1);
}).filter(function (value, index, self) {
    // http://stackoverflow./a/14438954/1789518
    return self.indexOf(value) === index;
});

var getLetters = function(items) {
    var letters = [];

    items.forEach(function(item) {
        if(letters.indexOf(item.title[0].toUpperCase()) === -1) {
            letters.push(item.title[0].toUpperCase());
        }
    });

    return letters;
};

getLetters([{title:"Apple"},{title:"Avocado"},{title:"Banana"},{title:"Cucumber"}]);

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