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I am very new to Javascript and am trying to translate a game i made in python into javascript. I am currently trying to get keyboard input for the game. Whenever i run this however it gives me the following error: Uncaught TypeError: Cannot read property '0' of undefined(at line 4 in this example)

Board is a 2d array used to store the board and i have tested that before the addEventListener statement Board is not undefined.

Why is this error happening and what should i do to fix it. As mentioned before i am a complete beginner at javascript so simple explanations would be greatly appreciated. Kind regards

I'm experienced with Pandas but stumbled upon a problem that I can't seem to figure out.

I have a large dataset ((40,000, 16)) and I am trying to group it by a specific column ("group_name" for this matter) and then for each group apply the following rules so it'd merge into one row per group:

• x1, x2, x3 are the "important" columns, if one row has less nulls than the others, take it. (see example with row D)
• If there are conflicts in any column, it's arbitrary and we can pick whatever.
• Combine the nulls on the important fields (x1, x2, x3), see example with row A.

Here is an example with 6 rows that should turn into 4 groups (aka 4 rows).

So far I have groups = df.groupby['group_name']

I tried many other solutions such as summing each group, applying a transformation, aggregating by each 'important' column, merging on each 'important' column and more. Each solution brought it's own problems so I'm offering this question here without limiting people to a certain way.

Also, I spent nearly two days combining different solutions from other questions but none has seem to work. Perhaps I've missed something.

• Please note that since this is a large dataset, I'd very much like to avoid using for loop on each group since efficiency is something to consider here.

I hope I explained everything properly, please let me know if something is unclear.

Code to re-create the dataframe (thanks to @Henry Ecker from the first answer):

I am trying to understand the constructor of a std::thread but fail to understand how parameter types are represented/handled. Judging from cppreference, a simplified constructor could be sketched as follows:

Please let me know if I have to provide any more code or explanations.

I am trying to execute validate, if validation not successful, confirm(Yes/No), and then save method for all selected rows in a for loop.

Requirement: I have show a success/failure message after looping through all selected rows. That means:

If 5 rows are selected (2 are valid and 3 are not valid) - got from myService.validate

It will ask if you still want to continue for 3 not valid records - myConfirmService.confirm

It should save those 2 valid records

If user selects 'Yes' in confirm window (lets says for 2 records), then it should save these 2 as well.

At the end - it will display success/failure message - alertService.success

What I want:

To fulfil what I described in the requirement

and The success/failure message should display only once after all record saved

component.ts:

I started reading things about java, jvm and so. But when it comes to perm gen memory i keep getting different answers. I really do not get it, and get confused more and more, because there are many explanations that are different. So, is perm gen part of heap or it is not ?

Well, I want to create an HTML template to create this:

But this are my results:

or this:

In some way a need to combine this to results. Here is my code:

I am trying to extract Hindi text from a PDF. I tried all the methods to exract from the PDF, but none of them worked. There are explanations why it doesn't work, but no answers as such. So, I decided to convert the PDF to an image, and then use pytesseract to extract texts. I have downloaded the Hindi trained data, however that also gives highly inaccurate text.

That's the actual Hindi text from the PDF (download link):

That's my code so far:

I'm trying to send verification emails when someone fills a form on my website and I'm achieving this using nodemailer.

And my node.js code looks like this:

As a Java beginner, I have read several articles and some answers regarding List on SO, but cannot see any explanations what List exactly is and when to use it? Could you please clarify this issue?