WEBVTT 00:00.400 --> 00:01.240 Hi everyone. 00:01.240 --> 00:02.080 Welcome back. 00:02.080 --> 00:05.920 Now let's move on to the next gatherer which is scan. 00:06.320 --> 00:11.320 This builds on the idea of fold but adds an extra layer of usefulness. 00:11.520 --> 00:18.280 It's like fold, except that instead of producing one final result, it emits intermediate result after 00:18.280 --> 00:19.800 every element in the stream. 00:19.800 --> 00:24.920 So when using fold, you only get the final accumulated result at the end of the stream. 00:24.920 --> 00:31.200 That's what we saw in the previous lecture, but with scan, after every element is processed, it emits 00:31.200 --> 00:34.520 the current accumulated value downstream. 00:34.520 --> 00:39.440 That means if you are summing numbers, you will see the running total of each addition being emitted 00:39.440 --> 00:40.720 to the downstream. 00:41.080 --> 00:47.720 Since scan produces intermediate results, it's perfect for live tracking metrics like running a total 00:47.720 --> 00:53.320 of movie durations, a cumulative average of ratings, or a progress counter. 00:53.320 --> 00:58.520 For example, if you're analyzing a list of movies, scan can show you how the total duration grows 00:58.640 --> 01:00.760 as each movie is processed. 01:00.760 --> 01:05.000 So to summarize, you can think of scan as a fold with visibility. 01:05.040 --> 01:10.560 It performs the same accumulation logic, but continuously emits partial results. 01:10.560 --> 01:13.720 This makes it ideal for scenarios like dashboards. 01:13.820 --> 01:20.580 progress bar, or running analytics where you want to see every step of the aggregation in real time. 01:20.660 --> 01:24.660 So here is a code example of scan the syntax and everything. 01:24.660 --> 01:27.420 As you can see, this is very similar to fold. 01:27.460 --> 01:29.820 You have the supplier and the buy function. 01:29.820 --> 01:34.940 But the only thing that's different is that for every movie that's been passed from the stream, it's 01:34.940 --> 01:39.380 going to be emitting the running total and you'll be able to see it in the console. 01:39.380 --> 01:44.500 So this helps you visualize how the total evolves as we stream through the data. 01:44.540 --> 01:47.260 Let's go back to the code and start exploring this in action. 01:47.300 --> 01:48.500 Let's go back to the code. 01:48.820 --> 01:50.340 And here I'm back in IntelliJ. 01:50.540 --> 01:55.940 So I'm going to be commenting out the fold operation so that our console looks cleaner. 01:56.140 --> 01:57.380 Let's go to the scan. 01:57.420 --> 02:02.780 Actually we can copy the same code that we wrote for the duration and then put it over here. 02:02.780 --> 02:06.020 So in the place of fold all you got to do is scan. 02:06.180 --> 02:10.540 But instead of collecting the result, what I'm going to do I'm going to be doing a for each. 02:10.940 --> 02:15.460 And then I'm going to give a running total and then print that running total in the console. 02:15.500 --> 02:15.780 Okay. 02:15.820 --> 02:17.580 So we don't need this logger anymore. 02:17.700 --> 02:18.300 There you go. 02:18.340 --> 02:19.900 It's not going to return anything. 02:20.060 --> 02:20.660 Take that off. 02:20.660 --> 02:21.300 So there you go. 02:21.340 --> 02:24.300 We have the scan ready actually. 02:24.340 --> 02:27.520 So let's go ahead and execute this so that you'll be able to see the result on the. 02:33.880 --> 02:34.520 Screen here. 02:34.520 --> 02:39.640 As you can see, for each and every movie, you will be able to see the value being growing little by 02:39.640 --> 02:39.920 little. 02:39.920 --> 02:41.720 So first one is 175. 02:41.920 --> 02:51.760 That's our first movie, and 175 plus 142 is 317 and 317 plus 154 is basically 471. 02:51.760 --> 02:58.840 And this is the beauty of scan where it's going to continuously emit as the gatherer is performing the 02:58.880 --> 03:00.640 summation in our use case. 03:00.640 --> 03:06.360 So it's the same concept for, uh, average ratings and the same concept for titles. 03:06.400 --> 03:08.480 Actually, we can actually explore one of them. 03:08.480 --> 03:11.600 Let's go here copy this and then put it over here. 03:11.600 --> 03:13.760 So in the place of this I'm going to do a scan. 03:14.000 --> 03:15.840 Take this off take this off. 03:15.840 --> 03:17.640 And then we can do for each. 03:17.680 --> 03:20.120 We can actually print the string over here okay. 03:20.160 --> 03:24.400 Let's run this program one more time so you can see that the title is growing one by one. 03:24.400 --> 03:29.840 It started with Godfather and then it added the next movie, it added the next movie, and the list 03:29.840 --> 03:30.840 goes on and on. 03:30.840 --> 03:32.400 So this is the beauty of scan. 03:32.440 --> 03:36.760 You have the ability to see where the accumulation is for each and every element. 03:36.760 --> 03:38.200 That's part of the stream. 03:38.200 --> 03:39.680 This marks the end of this lecture. 03:39.680 --> 03:40.680 Thank you for watching.