{"id":377,"date":"2020-12-20T17:06:11","date_gmt":"2020-12-20T16:06:11","guid":{"rendered":"https:\/\/mic.st\/blog\/?p=377"},"modified":"2021-01-25T07:56:07","modified_gmt":"2021-01-25T06:56:07","slug":"how-to-sort-an-array-of-objects-by-date-property","status":"publish","type":"post","link":"https:\/\/mic.st\/blog\/how-to-sort-an-array-of-objects-by-date-property\/","title":{"rendered":"How to sort an array of objects by date property"},"content":{"rendered":"\r\n

You might know the very handy sort(by:)<\/code> method in Swift that you can use to sort any kind of array. If not, see this as some kind of friendly introduction to you. Read carefully and I will teach you now how to sort an array of custom type objects by their date property \ud83d\ude42<\/p>\r\n\r\n\r\n\r\n

The sort(by:)<\/code> method is pretty well documented in Apple’s official documentation: https:\/\/developer.apple.com\/documentation\/swift\/array\/2296801-sort<\/a><\/p>\r\n\r\n\r\n\r\n

\"An\r\n
This has actually nothing to do with sorting something by date but these teabags are nicely sorted anyway \ud83d\ude05<\/figcaption>\r\n<\/figure>\r\n\r\n\r\n\r\n

In a lot of cases you just call someArray.sort()<\/code>. This will sort an array of elements conforming to Comparable<\/code> (e.g. Int<\/code>, String<\/code> and a lot of other type) in ascending order. If you want to sort it in ascending order you can just call someArray.sort(by: >)<\/code>. However, what if you have an array of some custom type that does not conform to Comparable<\/code> and you want to sort this array by a date<\/code> property this class has?<\/p>\r\n\r\n\r\n\r\n

A ComparisonResult<\/code> can be .orderedDescending<\/code>, .orderedAscending<\/code> or .orderedSame<\/code>. In order to sort our array of objects, we can just check these values.<\/p>\r\n\r\n\r\n\r\n

So how do we sort our array of objects by their date<\/code> property? You can either pass in your sorting logic directly to the sort(by:)<\/code> method or make your custom type conform to Comparable<\/code> (which is probably the cleaner way).<\/p>\r\n\r\n\r\n\r\n

The documentation for sort(by:)<\/code> says that you can basically do anything in the passed in closure to compare your array. So we can just do that to compare our two date properties. Thankfully, when using Date<\/code>, you get a comparison method for free. It is called Date.compare(_:)<\/code> and it’s great. You pass in two dates and get back a ComparisonResult<\/code>. This makes your code very readable without doing anything because ComparisonResult<\/code> can be either .orderedAscending<\/code>, .orderedDescending<\/code> or .orderedSame<\/code>.<\/p>\r\n\r\n\r\n\r\n

In the following you can see some examples for passing in your logic directly.<\/p>\r\n\r\n\r\n

myElements.sort<\/span>(by: { element1, element2 in<\/span>\r\n    let<\/span> comparisonResult = element1.date.compare(element2.date)\r\n    return<\/span> comparisonResult == .orderedDescending\r\n})<\/code><\/span>Code language:<\/span> Swift<\/span> (<\/span>swift<\/span>)<\/span><\/small><\/pre>\r\n\r\n\r\n
or if you prefer the shorter syntax using $<\/code>:<\/p>\r\n\r\n\r\n
contentForMonth.sort<\/span>(by: {\r\n    let<\/span> comparisonResult = $0<\/span>.date.compare($1<\/span>.date)\r\n    return<\/span> comparisonResult == .orderedDescending\r\n})<\/code><\/span>Code language:<\/span> Swift<\/span> (<\/span>swift<\/span>)<\/span><\/small><\/pre>\r\n\r\n\r\n
or even shorter:<\/p>\r\n\r\n\r\n
someArray.sort<\/span>(by: { $0<\/span>.date.compare($1<\/span>.date) == .orderedDescending })<\/code><\/span>Code language:<\/span> Swift<\/span> (<\/span>swift<\/span>)<\/span><\/small><\/pre>\r\n\r\n\r\n
Conforming to Comparable to easily sort an array of objects by date<\/h2>\r\n\r\n\r\n\r\n
Making a custom type conform to Comparable<\/code> is actually easier than you might think. You just have to define two protocol methods for that. Via the first method you define in which case one object can be seen as less than a second object. The second method is for defining equality of two objects.<\/p>\r\n\r\n\r\n\r\n
The benefit of going this way is that you can sort your array of custom type objects anywhere in your Swift project without passing in sorting logic anymore.<\/p>\r\n\r\n\r\n\r\n
In the following you see an implementation for a custom type RowModel<\/code> that has an optional Date<\/code> property. In this case, I added an additional method for unwrapping and comparing the two arguments. If your date<\/code> property is not optional you would not need that.<\/p>\r\n\r\n\r\n
extension<\/span> RowModel<\/span>: Comparable<\/span> <\/span>{\r\n\tstatic<\/span> func<\/span> < (lhs: RowModel, rhs: RowModel) -> Bool<\/span> <\/span>{\r\n\t\tif<\/span> let<\/span> result = compare(lhs, rhs), result == .orderedAscending {\r\n\t\t\treturn<\/span> true<\/span>\r\n\t\t}\r\n\t\treturn<\/span> false<\/span>\r\n\t}\r\n\r\n\tstatic<\/span> func<\/span> == (lhs: RowModel, rhs: RowModel)<\/span><\/span> -> Bool<\/span> {\r\n\t\tif<\/span> let<\/span> result = compare(lhs, rhs), result == .orderedSame {\r\n\t\t\treturn<\/span> true<\/span>\r\n\t\t}\r\n\t\treturn<\/span> false<\/span>\r\n\t}\r\n\r\n\tfileprivate<\/span> static<\/span> func<\/span> compare<\/span>(_<\/span> lhs: RowModel, _<\/span> rhs: RowModel)<\/span><\/span> -> ComparisonResult?<\/span> {\r\n\t\tif<\/span> let<\/span> lhsDate = lhs.date,\r\n\t\t   let<\/span> rhsDate = rhs.date {\r\n\t\t\treturn<\/span> lhsDate.compare(rhsDate)\r\n\t\t}\r\n\t\treturn<\/span> nil<\/span>\r\n\t}\r\n}<\/code><\/span>Code language:<\/span> Swift<\/span> (<\/span>swift<\/span>)<\/span><\/small><\/pre>\r\n\r\n\r\n
With this small addition you can shorten your calls for sorting an array to this:<\/p>\r\n\r\n\r\n
\/\/ Sort for descending order<\/span>\r\nsomeArray.sort(>)\r\n\r\n\/\/ Sort for ascending order<\/span>\r\nsomeArray.sort()<\/code><\/span>Code language:<\/span> JavaScript<\/span> (<\/span>javascript<\/span>)<\/span><\/small><\/pre>","protected":false},"excerpt":{"rendered":"
You might know the very handy sort(by:) method in Swift that you can use to sort any kind of array. If not, see this as some kind of friendly introduction to you. Read carefully and I will teach you now how to sort an array of custom type objects by their date property \ud83d\ude42 The…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"inline_featured_image":false,"footnotes":""},"categories":[3],"tags":[4,35],"class_list":["post-377","post","type-post","status-publish","format-standard","hentry","category-ios-development","tag-ios","tag-swift"],"_links":{"self":[{"href":"https:\/\/mic.st\/blog\/wp-json\/wp\/v2\/posts\/377","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/mic.st\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/mic.st\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/mic.st\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/mic.st\/blog\/wp-json\/wp\/v2\/comments?post=377"}],"version-history":[{"count":6,"href":"https:\/\/mic.st\/blog\/wp-json\/wp\/v2\/posts\/377\/revisions"}],"predecessor-version":[{"id":410,"href":"https:\/\/mic.st\/blog\/wp-json\/wp\/v2\/posts\/377\/revisions\/410"}],"wp:attachment":[{"href":"https:\/\/mic.st\/blog\/wp-json\/wp\/v2\/media?parent=377"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/mic.st\/blog\/wp-json\/wp\/v2\/categories?post=377"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/mic.st\/blog\/wp-json\/wp\/v2\/tags?post=377"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}