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What is tail recursion?
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1766
Consider a simple function that adds the first N natural numbers. (e.g. sum(5) = 1 + 2 + 3 + ...
How to emulate C array initialization “int arr[] = { e1, e2, e3, … }” behaviour with std::array?
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10 Answers
10
Active
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“Width equals height” constraint in Interface Builder
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187
Update Xcode 5.1b5
Ctrl+click and drag from a view and release while the pointer is over th...
How to get the clicked link's href with jquery?
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175
this in your callback function refers to the clicked element.
$(".addressClick").click(fun...
使用CSplitterWnd实现拆分窗口（多视图显示） - C/C++ - 清泛网 - 专注C/C++及内核技术
...用户可以缩放各行各列。一个静态拆分窗口最多可以包含16行16列。
要找一个使用了静态拆分窗口的应用程序，只要看一下windows管理器即可。
动态拆分窗口最多可以有两行两列，但它们可以相互拆分和合并。Vc就使用了动态拆...
How to navigate through a vector using iterators? (C++)
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112
You need to make use of the begin and end method of the vector class, which return the iterato...
Android ImageView Zoom-in and Zoom-Out
...ss Zoom extends View {
private Drawable image;
ImageButton img,img1;
private int zoomControler=20;
public Zoom(Context context){
super(context);
image=context.getResources().getDrawable(R.drawable.j);
//image=context.getResources().getDrawable(R...
How can I get a Bootstrap column to span multiple rows?
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167
For Bootstrap 3:
<link href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/css/boots...
Find the files existing in one directory but not in the other [closed]
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14 Answers
14
Active
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Drop data frame columns by name
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You can use a simple list of names :
DF <- data.frame(
x=1:10,
y=10:1,
z=rep(5,10),
a=11:20
)
drops <- c("x","z")
DF[ , !(names(DF) %in% drops)]
Or, alternatively, you can make a list of those to keep and refer to them by name :
keeps <- c("y", "a")
DF[keeps]
EDIT ...