1
00:00:00,590 --> 00:00:01,890
Welcome back.

2
00:00:01,910 --> 00:00:08,130
Let's talk about filter now based on the name you should guess what it does.

3
00:00:08,130 --> 00:00:16,020
It filters things for us so with map we always got the same number of items back right.

4
00:00:16,020 --> 00:00:23,480
We have three items and we got back three items we just mapped over each item with filter.

5
00:00:23,610 --> 00:00:26,840
We can sometimes receive less than what we gave it.

6
00:00:26,870 --> 00:00:35,480
We're filtering some of our results so let's create a new function instead of multiply by two.

7
00:00:35,500 --> 00:00:40,220
I want to create a function in this function.

8
00:00:40,220 --> 00:00:42,390
What are we going to do to the items.

9
00:00:42,500 --> 00:00:52,580
Let's say if items are check if odd so we're going to say hey are these numbers odd and only return

10
00:00:52,580 --> 00:00:53,900
the odd numbers.

11
00:00:53,900 --> 00:01:03,470
So check what is going to receive an item and this item is going to be acted upon.

12
00:01:03,630 --> 00:01:05,790
And once again we have to return something.

13
00:01:05,790 --> 00:01:08,610
What are we going to return.

14
00:01:08,610 --> 00:01:18,300
Well the filter function is going to try and receive a true and false value or a boolean value whether

15
00:01:18,300 --> 00:01:21,560
it should be filtered or it should not.

16
00:01:21,570 --> 00:01:31,470
So if we want to check if a number is on well we can say item modulo 2 because modulo 2 is going to

17
00:01:31,470 --> 00:01:32,930
divide the number by two.

18
00:01:33,120 --> 00:01:39,610
And if it equals zero then it's even right.

19
00:01:39,630 --> 00:01:42,870
So I can say doesn't equal zero.

20
00:01:42,870 --> 00:01:47,170
So if the remainder doesn't equal zero it's going to be odd.

21
00:01:47,370 --> 00:01:50,310
And we just simply return this.

22
00:01:50,570 --> 00:01:57,710
Again this is going to evaluate into a boolean expression and based on the boolean expression filter

23
00:01:57,710 --> 00:02:03,980
is going to say if it's true I'm going to keep it in the list if it's not I'm going to remove it or

24
00:02:04,220 --> 00:02:06,550
not add it to the new list.

25
00:02:06,650 --> 00:02:09,190
So let's check this out instead of map.

26
00:02:09,200 --> 00:02:10,630
Let's do a filter.

27
00:02:10,880 --> 00:02:17,310
And here we'll do check out or you know what I don't like this name.

28
00:02:17,340 --> 00:02:19,920
Let's do only odd

29
00:02:24,560 --> 00:02:34,560
if I run this look at that I've filtered and remove the too because that's an even number again.

30
00:02:34,610 --> 00:02:41,390
Notice here how I'm not calling the function because filter accepts a function or what we call a function

31
00:02:41,390 --> 00:02:47,690
signature that is hey just tell me where I can find what memory space I should go to for what action

32
00:02:47,690 --> 00:02:48,560
to take.

33
00:02:48,740 --> 00:02:55,200
And it's going to say hey give me the data and I'm going to go and run this function on each item.

34
00:02:55,730 --> 00:03:03,420
So when we go to one it's going to run this function with one as the argument one divided by two.

35
00:03:03,430 --> 00:03:06,160
Well that definitely doesn't give us a remainder of 0.

36
00:03:06,220 --> 00:03:08,110
So that's going to return true.

37
00:03:08,140 --> 00:03:14,740
And that means I'm going to add it to the new list that we create when we get to 2 though because this

38
00:03:14,800 --> 00:03:22,250
is going to return false it's not going to add it to the list again.

39
00:03:22,390 --> 00:03:29,650
If let's say we have a list of users in that case we might want to filter out based on user starting

40
00:03:29,650 --> 00:03:40,220
with the name A we can use the filter function to filter through all the user names and only have a

41
00:03:40,220 --> 00:03:46,970
new list with the user names with letters starting with a another very useful function.

42
00:03:46,970 --> 00:03:49,280
And as you can see we kept everything pure.

43
00:03:49,370 --> 00:03:56,040
It creates a new list for us it doesn't modify the original list so we're keeping that functional paradigm

44
00:03:56,190 --> 00:03:57,330
in mind.

45
00:03:57,390 --> 00:04:03,000
And once again the beauty with both map and filter is look how simple the functions become.

46
00:04:03,000 --> 00:04:05,100
Everything is just nice and simple.

47
00:04:05,100 --> 00:04:09,810
And mind you they can get a little bit more complicated about all we need to know is Hey what should

48
00:04:09,810 --> 00:04:13,560
I do to the item and why should I return.

49
00:04:13,560 --> 00:04:18,270
That's the only thing that they're concerned about instead of having these massive massive functions

50
00:04:18,270 --> 00:04:20,550
that tried to do everything.

51
00:04:20,570 --> 00:04:22,850
All right let's talk about zip next.