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sql - How to select the first row of each group?

I have a DataFrame generated as follow: df.groupBy($"Hour", $"Category") .agg(sum($"value") as " ... each group as well. Any help is highly appreciated. Question&Answers:os...

asked Oct 16, 2021 in Technique[技术] by 深蓝 (71.8m points)

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r - Understanding exactly when a data.table is a reference to (vs a copy of) another data.table

I'm having a little trouble understanding the pass-by-reference properties of data.table. Some operations seem to ... if someone could explain this to me. Question&Answers:os...

asked Oct 16, 2021 in Technique[技术] by 深蓝 (71.8m points)

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javascript - Capture HTML Canvas as gif/jpg/png/pdf?

Is it possible to capture or print what's displayed in an html canvas as an image or pdf? I'd like to ... and be able to generate a png from that image. Question&Answers:os...

asked Oct 16, 2021 in Technique[技术] by 深蓝 (71.8m points)

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What are all the uses of an underscore in Scala?

I've taken a look at the list of surveys taken on scala-lang.org and noticed a curious question: " ... please do so here. Explanatory examples are appreciated. Question&Answers:os...

asked Oct 16, 2021 in Technique[技术] by 深蓝 (71.8m points)

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How can I increment a date by one day in Java?

I'm working with a date in this format: yyyy-mm-dd. How can I increment this date by one day? Question&Answers:os...

asked Oct 16, 2021 in Technique[技术] by 深蓝 (71.8m points)

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Why is 128==128 false but 127==127 is true when comparing Integer wrappers in Java?

class D { public static void main(String args[]) { Integer b2=128; Integer b3=128; System.out.println(b2==b3 ... Note: Numbers between -128 and 127 are true. Question&Answers:os...

asked Oct 16, 2021 in Technique[技术] by 深蓝 (71.8m points)

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c++ - Meaning of 'const' last in a function declaration of a class?

What is the meaning of const in declarations like these? The const confuses me. class foobar { public: operator int () const; const char* foo() const; }; Question&Answers:os...

asked Oct 16, 2021 in Technique[技术] by 深蓝 (71.8m points)

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.net - What do Option Strict and Option Explicit do?

I saw this post: Typos Just use option strict and explicit please.. during one software development project, which I was ... it's Visual Basic, I'm doing PHP). Question&Answers:os...

asked Oct 16, 2021 in Technique[技术] by 深蓝 (71.8m points)

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error handling - Does a finally block always get executed in Java?

Considering this code, can I be absolutely sure that the finally block always executes, no matter what something() is? ... if this will get printed out"); } Question&Answers:os...

asked Oct 16, 2021 in Technique[技术] by 深蓝 (71.8m points)

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html - How to align 3 divs (left/center/right) inside another div?

I want to have 3 divs aligned inside a container div, something like this: [[LEFT] [CENTER] [RIGHT]] Container div is ... : [[LEFT] [CENTER] ] [RIGHT] Any tips? Question&Answers:os...

asked Oct 16, 2021 in Technique[技术] by 深蓝 (71.8m points)

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How to use the toString method in Java?

Can anybody explain to me the concept of the toString() method, defined in the Object class? How is it used, and what is its purpose? Question&Answers:os...

asked Oct 16, 2021 in Technique[技术] by 深蓝 (71.8m points)

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What's the canonical way to check for type in Python?

What is the best way to check whether a given object is of a given type? How about checking whether the object inherits ... How do I check whether it's a str? Question&Answers:os...

asked Oct 16, 2021 in Technique[技术] by 深蓝 (71.8m points)

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javascript - Client on Node.js: Uncaught ReferenceError: require is not defined

I am writing an application with the Node.js, Express.js, and Jade combination. I have file client.js, which is ... js file that opens the socket to the server? Question&Answers:os...

asked Oct 16, 2021 in Technique[技术] by 深蓝 (71.8m points)

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python - Pandas: how to merge two dataframes on a column by keeping the information of the first one?

I have two dataframes df1 and df2. df1 contains the information of the age of people, while df2 contains the information of ... 44 F 3 Jack 27 M 4 Laura 30 NaN Question&Answers:os...

asked Oct 16, 2021 in Technique[技术] by 深蓝 (71.8m points)

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1 answer

javascript - Correct modification of state arrays in React.js

I want to add an element to the end of a state array, is this the correct way to do it? this.state. ... copy of the array, and setStateing that seems wasteful. Question&Answers:os...

asked Oct 16, 2021 in Technique[技术] by 深蓝 (71.8m points)

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375 views

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I do not want to inherit the child opacity from the parent in CSS

I do not want to inherit the child opacity from the parent in CSS. I have one div which is the parent, and ... inherit the opacity property. How can I do that? Question&Answers:os...

asked Oct 16, 2021 in Technique[技术] by 深蓝 (71.8m points)

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r - Subset data frame based on number of rows per group

I have data like this, where some "name" occurs more than three times: df <- data.frame(name = c("a", "a" ... frame(table(unique(df)$name)) subset(df, name > 3) Question&Answers:os...

asked Oct 16, 2021 in Technique[技术] by 深蓝 (71.8m points)

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1 answer

function - Why are Python lambdas useful?

Closed. This question needs to be more focused. It is not currently accepting answers. Question&Answers:os...

asked Oct 16, 2021 in Technique[技术] by 深蓝 (71.8m points)

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datetime - Find objects between two dates MongoDB

I've been playing around storing tweets inside mongodb, each object looks like this: { "_id" : ObjectId(" ... the dates are stored in a specific format? Question&Answers:os...

asked Oct 16, 2021 in Technique[技术] by 深蓝 (71.8m points)

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192 views

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php - How to get WooCommerce order details

In WooCommerce from the following line code: $order = new WC_Order( $order_id ); How can I get WooCommerce order details from the order id? Question&Answers:os...

asked Oct 16, 2021 in Technique[技术] by 深蓝 (71.8m points)

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python - How to pass arguments to a Button command in Tkinter?

Suppose I have the following Button made with Tkinter in Python: import Tkinter as Tk win = Tk.Toplevel( ... immediately, and pressing the button does nothing. Question&Answers:os...

asked Oct 16, 2021 in Technique[技术] by 深蓝 (71.8m points)

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How do I load an HTTP URL with App Transport Security enabled in iOS 9?

This question already has answers here: Question&Answers:os...

asked Oct 16, 2021 in Technique[技术] by 深蓝 (71.8m points)

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81 views

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What does android:layout_weight mean?

I don't understand how to use this attribute. Can anyone tell me more about it? Question&Answers:os...

asked Oct 16, 2021 in Technique[技术] by 深蓝 (71.8m points)

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181 views

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php - How to squeeze error message out of PDO?

This question already has an answer here: Question&Answers:os...

asked Oct 16, 2021 in Technique[技术] by 深蓝 (71.8m points)

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Get the current URL with JavaScript?

All I want is to get the website URL. Not the URL as taken from a link. On the page loading I need to be able ... set it as a variable to do with as I please. Question&Answers:os...

asked Oct 16, 2021 in Technique[技术] by 深蓝 (71.8m points)

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358 views

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jQuery callback on image load (even when the image is cached)

I want to do: $("img").bind('load', function() { // do stuff }); But the load event doesn't fire when ... docs suggest a plugin to fix this, but it doesn't work Question&Answers:os...

asked Oct 16, 2021 in Technique[技术] by 深蓝 (71.8m points)

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98 views

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How can I do string interpolation in JavaScript?

Consider this code: var age = 3; console.log("I'm " + age + " years old!"); Are there any other ... a variable in to a string, apart from string concatenation? Question&Answers:os...

asked Oct 16, 2021 in Technique[技术] by 深蓝 (71.8m points)

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92 views

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android - How to start new activity on button click

In an Android application, how do you start a new activity (GUI) when a button in another activity is ... do you pass data between these two activities? Question&Answers:os...

asked Oct 16, 2021 in Technique[技术] by 深蓝 (71.8m points)

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