[<< Day 8](../08_Day_Objects/08_day_objects.md) | [Day 10 >>](../10_Day_Sets_and_Maps/10_day_Sets_and_Maps.md)
@ -181,7 +182,7 @@ Instead of writing regular loop, latest version of JavaScript introduced lots of
_forEach_: Iterate an array elements. We use _forEach_ only with arrays. It takes a callback function with elements, index parameter and array itself. The index and the array optional.
```js
arr.forEach(function(element, index, arr) {
arr.forEach(function(element, index, arr) {
console.log(index, element, arr)
})
// The above code can be written using arrow function
@ -222,7 +223,7 @@ console.log(sum)
```js
const countries = ['Finland', 'Denmark', 'Sweden', 'Norway', 'Iceland']
const areAllStr = names.some(name => typeof name === 'number')
const areAllStr = names.some((name) => typeof name === 'number')
console.log(areAllStr) // false
```
### sort
_sort_: The sort methods arranges the array elements either ascending or descending order. By default, the **_sort()_** method sorts values as strings.This works well for string array items but not for numbers. If number values are sorted as strings and it give us wrong result. Sort method modify the original array. It is recommended to copy the original data before you start using _sort_ method.
@ -506,13 +506,13 @@ As you can see in the example below, 100 came first after sorted in ascending or
const numbers = [9.81, 3.14, 100, 37]
// Using sort method to sort number items provide a wrong result. see below
When ever we sort objects in an array. We use the object key to compare. Lets see the example below.
```js
objArr.sort(function(a, b) {
objArr.sort(function(a, b) {
if (a.key <b.key)return-1
if (a.key > b.key) return 1
return 0
@ -531,7 +531,7 @@ objArr.sort(function(a, b) {
// or
objArr.sort(function(a, b) {
objArr.sort(function(a, b) {
if (a['key'] <b['key'])return-1
if (a['key'] > b['key']) return 1
return 0
@ -541,7 +541,7 @@ const users = [
{ name: 'Asabeneh', age: 150 },
{ name: 'Brook', age: 50 },
{ name: 'Eyo', age: 100 },
{ name: 'Elias', age: 22 }
{ name: 'Elias', age: 22 },
]
users.sort((a, b) => {
if (a.age <b.age)return-1
@ -568,7 +568,7 @@ const products = [
{ product: 'potato', price: ' ' },
{ product: 'avocado', price: 8 },
{ product: 'coffee', price: 10 },
{ product: 'tea', price: '' }
{ product: 'tea', price: '' },
]
```
@ -587,17 +587,17 @@ const products = [
13. Use **_filter_** to filter out countries containing six letters and more in the country array.
14. Use **_filter_** to filter out country start with 'E';
15. Use **_filter_** to filter out only prices with values.
18. Declare a function called getStringLists which takes an array as a parameter and then returns an array only with string items.
19. Use **_reduce_** to sum all the numbers in the numbers array.
20. Use **_reduce_** to concatenate all the countries and to produce this sentence: **_Estonia, Finland, Sweden, Denmark, Norway, and IceLand are north European countries_**
21. Explain the difference between **_some_** and **_every_**
22. Use **_some_** to check if some names' length greater than seven in names array
23. Use **_every_** to check if all the countries contain the word land
24. Explain the difference between **_find_** and **_findIndex_**.
25. Use **_find_** to find the first country containing only six letters in the countries array
26. Use **_findIndex_** to find the position of the first country containing only six letters in the countries array
27. Use **_findIndex_** to find the position of **_Norway_** if it doesn't exist in the array you will get -1.
28. Use **_findIndex_** to find the position of **_Russia_** if it doesn't exist in the array you will get -1.
16. Declare a function called getStringLists which takes an array as a parameter and then returns an array only with string items.
17. Use **_reduce_** to sum all the numbers in the numbers array.
18. Use **_reduce_** to concatenate all the countries and to produce this sentence: **_Estonia, Finland, Sweden, Denmark, Norway, and IceLand are north European countries_**
19. Explain the difference between **_some_** and **_every_**
20. Use **_some_** to check if some names' length greater than seven in names array
21. Use **_every_** to check if all the countries contain the word land
22. Explain the difference between **_find_** and **_findIndex_**.
23. Use **_find_** to find the first country containing only six letters in the countries array
24. Use **_findIndex_** to find the position of the first country containing only six letters in the countries array
25. Use **_findIndex_** to find the position of **_Norway_** if it doesn't exist in the array you will get -1.
26. Use **_findIndex_** to find the position of **_Russia_** if it doesn't exist in the array you will get -1.
### Exercises: Level 2
@ -614,90 +614,94 @@ const products = [
1. Use the countries information, in the data folder. Sort countries by name, by capital, by population
1. \*\*\* Find the 10 most spoken languages:
````js
// Your output should look like this
console.log(mostSpokenLanguages(countries, 10))
[(91, 'English'),
(45, 'French'),
(25, 'Arabic'),
(24, 'Spanish'),
(9, 'Russian'),
(9, 'Portuguese'),
(8, 'Dutch'),
(7, 'German'),
(5, 'Chinese'),
(4, 'Swahili'),
(4, 'Serbian')]
// Your output should look like this
console.log(mostSpokenLanguages(countries, 3))
[
(91, 'English'),
(45, 'French'),
(25, 'Arabic')
]```
````
````js
// Your output should look like this
console.log(mostSpokenLanguages(countries, 10))
[
{country: 'English',count:91},
{country: 'French',count:45},
{country: 'Arabic',count:25},
{country: 'Spanish',count:24},
{country:'Russian',count:9},
{country:'Portuguese', count:9},
{country:'Dutch',count:8},
{country:'German',count:7},
{country:'Chinese',count:5},
{country:'Swahili',count:4},
{country:'Serbian',count:4}
]
// Your output should look like this
console.log(mostSpokenLanguages(countries, 3))
[
{country: 'English',count: 91},
{country: 'French',count: 45},
{country: 'Arabic',count: 25},
]```
````
1. \*\*\* Use countries_data.js file create a function which create the ten most populated countries
{country: 'United States of America', population: 323947000}
]
```
````
1. \*\*\* Try to develop a program which calculate measure of central tendency of a sample(mean, median, mode) and measure of variability(range, variance, standard deviation). In addition to those measures find the min, max, count, percentile, and frequency distribution of the sample. You can create an object called statistics and create all the functions which do statistical calculations as method for the statistics object. Check the output below.
Asabeneh
4 years ago