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Checking if an Android application is running in the background
By background, I mean none of the application's activities are currently visible to the user?
30 Answers
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Applying a function to every row of a table using dplyr?
When working with plyr I often found it useful to use adply for scalar functions that I have to apply to each and every row.
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...统有了解，淘宝的秒杀活动，本质上是用输验证码并在CDN上把用户直接过滤掉了，比如：1千万个用户过滤了只剩2万个用户，这样数据库就顶得住了）
其三，有人拿这个系统和奥运会的票务系统比较。我觉得还是不一样。虽...
Remove sensitive files and their commits from Git history
I would like to put a Git project on GitHub but it contains certain files with sensitive data (usernames and passwords, like /config/deploy.rb for capistrano).
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What is the difference between graph search and tree search?
What is the difference between graph search and tree search versions regarding DFS, A* searches in artificial intelligence ?
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Difference between DateTime and Time in Ruby
What's the difference between DateTime and Time classes in Ruby and what factors would cause me to choose one or the other?
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When would anyone use a union? Is it a remnant from the C-only days?
I have learned but don't really get unions. Every C or C++ text I go through introduces them (sometimes in passing), but they tend to give very few practical examples of why or where to use them. When would unions be useful in a modern (or even legacy) case? My only two guesses would be programming ...
The new keyword “auto”; When should it be used to declare a variable type? [duplicate]
Have we (as a community) had enough experience to determine when and/or whether auto is being abused?
6 Answers
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How dangerous is it to compare floating point values?
I know UIKit uses CGFloat because of the resolution independent coordinate system.
11 Answers
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Java “Virtual Machine” vs. Python “Interpreter” parlance?
It seems rare to read of a Python "virtual machine" while in Java "virtual machine" is used all the time.
13 Answers
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