MongoDB Tutorial 4 Map Reduce Finalize Group

I received a bunch of questions about using Map Reduce in MongoDB, so here I provide a bunch of examples. First I'll cover Map Reduce using straight JavaScript. Then we'll cover increasingly complex MongoDB Map Reduce queries. Then finally I'll cover using Group and Distinct.

[kemchobhenchod]

"I have a lot to do, so let's get into it!"
should be every programmer's anthem

[not-lain]

really liked the easter egg at 5:14 professor : "Paul Slugma"

[hamzaaitboutou]

Thanks again! super useful tutorial as usual. I have a question though: following your example of counting classes a student is enrolled in given the map function for that and entity Student, which is a good practice: 1) emit whole student object, o or 2) emit only student id and then fetch students by id later?

[SKAnanitoS]

this tutorial was really good! the only thing I would like to mention is that it would be nice to have another video with MongoDB injection attacks and techniques that we can use to avoid them.

[RishinderRana]

Great tutorial! I believe the only part missing is to cover this in a partitioned architecture. Do we need to perform this on all partitions and then aggregate the final results or there's something that Mongo provides to assist with such situations?

[timharris]

Thanks for posting the code on the website. This was a really helpful tutorial!

[KrausBean]

So, these Map Reduce functions are creating a new DB to hold the output? Is that common practice with MongoDB? Is that how it should be handled if you had different document types or models (Students, Assignments, etc.)?

[santoshbaggam]

hi Derek, fabulous tuts.. I'd just want to learn more on MongoDb GeoIndexing.. can you upload a vid explaining various use cases.. eg: nearby store locations, Uber taxi vehicle tracking, etc.. would be a great one to watch. thanks in advance :)

[hgflame]

Thanks! Loved the comparison part, helps greatly in understanding.

[viquarahmed]

hi derek... I hope next videos are angular js and R programming tutorials.BTW congratulations for completing Mongodb tutorials series.

[tejapolisetty]

flow of arguments in mapfunc and reducefunction, can you please explain?

[pjmclenon]

hello mr derek..i do not see the sharding and replicas example that you said in vid 1...thanxz alot jessica

[masoud]

really nice and educational, well done

[skondgekar]

These are really great tutorials within such less time. Great efforts.
Can you please show us a way to take mongodb backup and restore? And suggest any opensource admin ui similer to phpmyadmin.

[orimorningstar]

Even on Christmas Eve you film and code :O

[shwedaz]

Great videos! Would be even better if there was at least one real life application example where we could use MangoDB. Let's say - simple login system, or article class, or anything, but real, not abstract, not doesn't even need to be simple. Thank you!

[AshfaqKhan-fqgx]

How to export a file in mongoDB to a csv format? I've tried few commands but went in vain. Appreciate your work!

[klausvonshnytke]

I find it rather depressing that there are so few tutorials about jboss fuse. Even those on the official website are not very technical. Would you mind recording something on this subject?

[suibora]

ples help me, ik this is unrelated but my progress has stopped because of this. i looked everywhere on the world wide web(stackoverflow) but came out with more questions than answers

Android development. i want to save an arraylist of custom objects after an app has exited.

i have watched the video on it and i can save the array list if android decides to close the app, but not if the user decides to.

how would i save an array list of custom objects to shared preferences. or is there another way entirely to save arraylists if user decides to close an app.

i tried converting the list to a set and saving it that way but no luck.

[regulus]

hi could you help with gridFS tutorial, to store images etc in mongo db please