# Dictionary Of Algorithms And Knowledge Structures

## Chapter 4data Structures: Objects And Arrays

Accessing the individual characters in a string appears like accessing array components (with a caveat that we’ll focus on in Chapter 5). Some very useful ones are slice and indexOf, which resemble the array strategies of the identical name. This is a direct translation of the ϕ formulation into JavaScript. Math.sqrt is the sq. root operate, as offered by the Math object in a standard JavaScript setting. We have to add two fields from the desk to get fields like n1• as a result of the sums of rows or columns usually are not saved directly in our data construction.

To discover out what properties an object has, you can use the Object.keys function. You give it an object, and it returns an array of strings—the item’s property names. A set of every day log entries can be represented as an array. But the entries do not encompass only a quantity or a string—each entry needs to store an inventory of actions and a Boolean worth that signifies whether or not Jacques became a squirrel or not.

### Databases

Ideally, we wish to group these collectively into a single worth and then put those grouped values into an array of log entries. Both string and array values contain, along with the size property, numerous properties that maintain operate values.

## Knowledge Structures

It accommodates cos , sin , and tan , in addition to their inverse features, acos, asin, and atan, respectively. The quantity π —or a minimum of the closest approximation that matches in a JavaScript quantity—is available as Math.PI. There is an old programming custom of writing the names of fixed values in all caps.

The types of values discussed in earlier chapters, corresponding to numbers, strings, and Booleans, are all immutable—it’s impossible to vary values of those varieties. You can combine them and derive new values from them, however if you take a selected string value, that value will all the time stay the identical. If you could have a string that incorporates “cat”, it’s not attainable for different code to alter a character in your string to make it spell “rat”.