大约有 32,000 项符合查询结果（耗时：0.0393秒） [XML]
dplyr summarise: Equivalent of “.drop=FALSE” to keep groups with zero length in output
...e to go with @Moody_Mudskipper's answer: Using .drop=FALSE can give potentially unexpected results when one or more grouping variables are not coded as factors. See examples below:
library(dplyr)
data(iris)
# Add an additional level to Species
iris$Species = factor(iris$Species, levels=c(levels(ir...
Boolean operators && and ||
...es the longer form "appropriate for programming control-flow and [is] typically preferred in if clauses."
So you want to use the long forms only when you are certain the vectors are length one.
You should be absolutely certain your vectors are only length 1, such as in cases where they are funct...
Objective-C: Where to remove observer for NSNotification?
...his is obviously not a satisfying answer.
I'd recommend, that you add a call [notificationCenter removeObserver: self] in method dealloc of those classes, which you intend to use as observers, as it is the last chance to unregister an observer cleanly. This will, however, only protect you against ...
Any way to write a Windows .bat file to kill processes? [closed]
...out of my IDE. Yes, these are processes from programs that my company installs on my machine for security and compliance. What I'd like to do is have a .bat file or script of some kind with which I can kill the processes in question.
...
How to alter SQL in “Edit Top 200 Rows” in SSMS 2008
...swered Jan 5 '10 at 8:29
David HallDavid Hall
30.2k1010 gold badges8484 silver badges119119 bronze badges
...
How do you find the current user in a Windows environment?
...
The extra information with all the environment variables makes this a wonderful extended answer.
– bballdave025
May 21 at 19:32
...
Git: How to rebase to a specific commit?
...
For me, this doesn't actually do what's intended. As far as I can tell, it tries to rebase onto the "last common ancestor" of topic and commitB.
– Dan Lenski
Jan 26 '15 at 18:20
...
Remove duplicate values from JS array [duplicate]
...olution is O(n^2), making it inefficient.
– Casey Kuball
Sep 21 '17 at 16:35
4
I really wish in 2...
How to send email from Terminal?
...
Note all this solutions assume you have a locally installed MTA
– Miquel
Nov 24 '11 at 18:07
11
...
What is a “slug” in Django?
When I read Django code I often see in models what is called a "slug". I am not quite sure what this is, but I do know it has something to do with URLs. How and when is this slug-thing supposed to be used?
...