Ruby map nested array

An array is an ordered list of elements that can be of any type. You can define an array by placing a list of elements between brackets like so:. You'll notice that the above array has strings, an integer, and a float. Arrays can have anything in them even other arrays! Now we need to save this array in a variable so we can play with it. Arrays are what we call indexed lists.

That means that each slot in an array is numbered. You can reference any element by its index number. The syntax to do this is typing the array name with the index in brackets [] directly following. Let's try it out. Are you surprised? You probably thought that you were going to get the number 4. That's because all array indices start with the number 0.

Try this in irb. Let's say you wanted to add or remove something from an array. There are a few methods that will help you perform these operations.

ruby map nested array

If you'd like to take the last item off of an array permanently, you can use the pop method. Note that when we called the pop method, the original array variable was modified ie, this is a method that mutates the callerbut the returned value is the popped element, as shown in the first line above.

This is a critical distinction to understand. Make sure you distinguish between the returned value by an expression, and what the expression is actually doing. If you'd like to add that item back to the array permanently, you can use the push method and send it the parameters you'd like to add.

Often you'll have an array and you'll want to operate on many of the elements in the array the same way. Ruby has many methods that do these type of operations. The map method iterates over an array applying a block to each element of the array and returns a new array with those results.

The irb session below shows how to use map to get the square of all numbers in an array. The collect method is an alias to map - they do the same thing. You'll notice that after performing these methods there is no change to the initial array. These methods are not destructive i.The most basic form of sorting is provided by the Ruby sort method, which is defined by the Enumerable module.

Notice that sort will return a new array with the results. This means that the original array will change instead of creating a new one, which can be good for performance. It is also possible to do custom sorting using the regular sort method with a block. It should return 1 greater than0 equal or -1 less than. You are not limited to sorting arraysyou can also sort a hash. You may want to sort something by multiple attributes, meaning that you first sort by date for examplebut because you have multiple things with the same date then you have a tie.

Where you set the primary sorting attribute as the first element of the array event. The idea of quick sort is to pick one number at random then divide the list we are sorting into two groups. Your quicksort implementation will not deal properly with arrays containing duplicates, as the pivot element number is only included once.

No need for "s. Sorting an array in Ruby is easy! Ruby Methods The most basic form of sorting is provided by the Ruby sort method, which is defined by the Enumerable module. An array of sorted elements! Sort in Reverse Order What about sorting in reverse? Example : music. How to Sort Hashes in Ruby You are not limited to sorting arraysyou can also sort a hash.

You get a multi-dimensional array when sorting a hash. Sorting By Multiple Values You may want to sort something by multiple attributes, meaning that you first sort by date for examplebut because you have multiple things with the same date then you have a tie. To break the tie you can use a secondary attribute.

ruby map nested array

Then we just repeat this operation until the list is sorted.It means that Ruby has support for higher-order functionsand functional programming. The way the map method works in Ruby is, it takes an enumerable objecti.

Then, for each of the elements in the enumerable, it executes the block, passing it the current element as an argument. The result of evaluating the block is then used to construct the resulting array. Applying map on an array returns a new array where each element is the result of evaluating the block with the element as an argument. As you can see, the block plays the role of the function in Ruby. In this example, the block i.

It will return a new array. If you want to change the values of the initial array, you can use map! The resulting array could contain a few nil values, and you might want to get rid of them.

ruby map nested array

Here are a few ways you could do it. Sometimes you need an index. Maybe you want to append the index to the value. Or maybe you have a better reason :. You use map to collect the result of running the block over the elements of the array. And you use each to run the block over the elements without collecting the values.

You can read more about using the each method here. They are aliases for each other, so there is no difference. What select does is it returns all the objects for which the block returns a truthy value i. If you liked this article, please take a moment and say thanks by sharing it on your favorite social media channel.

Posted by Cezar Halmagean. How to Use the Ruby Map Method.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service.

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How to Use The Ruby Map Method (With Examples)

I want to iterate over each "cell" and change the value to something else. How can I do this without flattening the array and recomposing. Something like:. The above method doesn't exactly turn out how I would think the random letter's work, but each row has the same random letters as the last row, in the same order. If you want to retain the object id of each array and change the content, then you can use replace.

Learn more. How to map over a nested array Ask Question. Asked 6 years, 9 months ago. Active 6 years, 9 months ago. Viewed 7k times. Steven Harlow Steven Harlow 7 7 silver badges 25 25 bronze badges. Active Oldest Votes. You don't need indexing at all.

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Feedback on Q2 Community Roadmap. Technical site integration observational experiment live on Stack Overflow. Dark Mode Beta - help us root out low-contrast and un-converted bits. Visit chat.Array indexing starts at 0, as in C or Java. A negative index is assumed to be relative to the end of the array—that is, an index of -1 indicates the last element of the array, -2 is the next to last element in the array, and so on.

A new array can be created by using the literal constructor []. Arrays can contain different types of objects. For example, the array below contains an Integera String and a Float:. An array can also be created by explicitly calling ::new with zero, one the initial size of the Array or two arguments the initial size and a default object.

ruby map nested array

Note that the second argument populates the array with references to the same object. Therefore, it is only recommended in cases when you need to instantiate arrays with natively immutable objects such as Symbols, numbers, true or false.

To create an array with separate objects a block can be passed instead. This method is safe to use with mutable objects such as hashes, strings or other arrays:.

In addition to the methods it mixes in through the Enumerable module, the Array class has proprietary methods for accessing, searching and otherwise manipulating arrays. Elements in an array can be retrieved using the [] method. It can take a single integer argument a numeric indexa pair of arguments start and length or a range. Negative indices start counting from the end, with -1 being the last element. Another way to access a particular array element is by using the at method.

The slice method works in an identical manner to []. To raise an error for indices outside of the array bounds or else to provide a default value when that happens, you can use fetch. The special methods first and last will return the first and last elements of an array, respectively. To return the first n elements of an array, use take.

Arrays keep track of their own length at all times. To query an array about the number of elements it contains, use lengthcount or size. Items can be added to the end of an array by using either push or. With insert you can add a new element to an array at any position.

Using the insert method, you can also insert multiple values at once:. The method pop removes the last element in an array and returns it:. To retrieve and at the same time remove the first item, use shift :. To delete a particular element anywhere in an array, use delete :. A useful method if you need to remove nil values from an array is compact :. It has the non-destructive uniqand destructive method uniq!

Like all classes that include the Enumerable module, Array has an each method, which defines what elements should be iterated over and how.An array is like a list but in code form.

It is a way for your program to store pieces of data as a collection. Arrays can contain any combination of Ruby data types -- booleans, integers, strings, or even other collections in the form of nested arrays and hashes. Arrays are declared as a comma-separated list of variable names or literal values wrapped in square brackets.

For example:.

Nested Arrays, Hashes & Loops in Ruby

We know that arrays can contain any type of data, including other arrays. Let's see that in action:. Nested arrays are useful for storing groups of similar data. Google Maps provides a JavaScript function that you, the developer, can use to add Google Maps to your own website. Don't worry about JavaScript right now; just understand that a JavaScript function is like a Ruby method. The map-making function or method, as we're going to think of it was designed to take in an argument of a nested array -- an array in which each index element is an array containing a place name, latitude, and longitude.

In other words, something that looks like this:. To access data from and add data to i. To grab an element out of the students array, we use bracket notation plus the index number of the element we want. The returned element is an array that looks like this:. Let's try a different example. Give it a shot in IRB before reading on. That element happens to be an array with three elements, the second of which the element at index 1 is the grade level of the student.

Now that we are getting comfortable retrieving data from a nested array, let's work on adding data to such an array. To illustrate, let's add another piece of info, "Class President"to the nested array that describes Monique.

What if we want to add data to every array that is nested within the parent array? When we are dealing with a one-dimensional array and want to do something to every element, we iterate, using methods like each and collect. If, for example, we wanted to puts out every member of the students array, we could do so like this:.

In order to manipulate or operate on each element of a nested array, we must first dig down into that level of the array. For example, run the following code in IRB:. If we want to iterate through the elements inside each child array, we add a second layer of iteration inside the first:. Let's take a look at some multidimensional arrays that have an even deeper nesting structure than the 2D examples we've seen so far. In this array, we have the top-level, or parent array, containing two child arrays.

The array that is the second element of the parent array contains eight elements, the last of which is another third-level array.

How to Use the Ruby Map Method

Here, we have three levels of nesting.Arrays and hashes are common data types used to store information. The main difference between an array and a hash is the manner in which data is stored. Arrays, represented by square brackets, contain elements which are indexed beginning at 0.

A nested array is exactly as it sounds — an array with one or more arrays nested inside of it. Nested arrays are useful when storing things in multiple categories. There can be multiple levels of nesting. If we want to dip into the inner arrays, we need to add an extra index for the inner array. For example:. It skipped the third layer i. The number of nested loops we need will correspond to the number of layers we wish to access.

If we wanted to loop through just the third layer, we would use a third nested loop:. Nested hashes can be a bit more complicated. A simple example of this is a dictionary.

Dictionary would be the hash, each word would be a key, and the definition would be its corresponding value. The syntax looks something like this:. In programming, we rarely use such a simple example. For example, say we wanted to store our holiday supplies by holiday and by season, we may end up with something that looks more like this:.

Accessing keys and values in a nested hash works the same way. If we wanted to find out which supplies we need for a specific holiday, things change a bit. Instead of entering one key, we need to enter two keys:. Just like we had to add a second level to our above index to access the innermost values in the hash, we likewise need to add a second loop to access and manipulate the innermost values.

Say we wanted to print each of the supplies we need for all seasons to prepare for the upcoming year, we would want to use nested loops:. Inner values; inner loop. Another example for the use of nested loops would be for comparison purposes. Say we have a tweet that is over characters and we need to shorten some of the words to make it fit. We have a list of common words and their abbreviations in a hash, and we need to figure out how to loop through the tweet and replace any of the matching words.


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