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dplyr summarise: Equivalent of “.drop=FALSE” to keep groups with zero length in output
...pecially since your data are already factored, you can use complete from "tidyr" to get what you might be looking for:
library(tidyr)
df %>%
group_by(b) %>%
summarise(count_a=length(a)) %>%
complete(b)
# Source: local data frame [3 x 2]
#
# b count_a
# (fctr) (int)
# 1 ...
Can't compare naive and aware datetime.now()
... var channelOptions = {
tags: "".split(" "),
id: "1"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function() {
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How to cancel a Task in await?
...y unchanged since then) and the Task-Based Asynchronous Pattern, which provides guidelines on how to use CancellationToken with async methods.
To summarize, you pass a CancellationToken into each method that supports cancellation, and that method must check it periodically.
private async Task TryT...
Vim: What's the difference between let and set?
...all options in effect.
:set tw=40
Will work as a shorthand for set textwidth=40
:set wrap&
Will set the default value for option wrap
:set nowrap
Will unset the option
:set wrap!
Will toggle the option
Most importantly,
:setTab # to get tab completion!
Few of the above can ...
Difference between Pragma and Cache-Control headers?
...ure, you must first check with me that it is up-to-date (i.e. perform revalidation)".
– clime
Mar 7 '13 at 14:03
...
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
...ntWnd, int nRows, int nCols, DWORD dwStyle = WS_CHILD | WS_VISIBLE, UINT nID = AFX_IDW_PANE_FIRST );
函数有5个参数，意义如下:
● pParentWnd:切分窗口的父窗口指针
● nRows:水平方向分隔窗口的数目
● nCols:垂直方向分隔窗口的数目 ...
What is the difference between server side cookie and client side cookie?
...creating cookies on the server and on the client? Are these called server side cookies and client side cookies? Is there a way to create cookies that can only be read on the server or on the client?
...
When is memoization automatic in GHC Haskell?
... indicates. This can be problematic in some situations. For example, consider the function
f = \x -> let y = [1..30000000] in foldl' (+) 0 (y ++ [x])
GHC might notice that y does not depend on x and rewrite the function to
f = let y = [1..30000000] in \x -> foldl' (+) 0 (y ++ [x])
In t...
what is the difference between ?:, ?! and ?= in regex?
...ing group and analyse each behaviour.
() capturing group - the regex inside the parenthesis must be matched and the match create a capturing group
(?:) non capturing group - the regex inside the parenthesis must be matched but doesn't not create the capturing group
(?=) positive look ahead - a...
Why XML-Serializable class need a parameterless constructor
...tialize it during deserialization.
Since you are using xml, you might consider using DataContractSerializer and marking your class with [DataContract]/[DataMember], but note that this changes the schema (for example, there is no equivalent of [XmlAttribute] - everything becomes elements).
Update: ...