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How do I perform the SQL Join equivalent in MongoDB?
...ttps://docs.mongodb.org/master/reference/operator/aggregation/lookup/#pipe._S_lookup
From the docs:
{
$lookup:
{
from: <collection to join>,
localField: <field from the input documents>,
foreignField: <field from the documents of the "from" collection>...
Declaring variables inside or outside of a loop
....Test extends java.lang.Object{
public inside.Test();
Code:
0: aload_0
1: invokespecial #1; //Method java/lang/Object."<init>":()V
4: return
public static void main(java.lang.String[]);
Code:
0: invokestatic #2; //Method java/lang/System.currentTimeMillis:()J
3...
What is the difference between join and merge in Pandas?
...andas as pd
left = pd.DataFrame({'key': ['foo', 'bar'], 'val': [1, 2]}).set_index('key')
right = pd.DataFrame({'key': ['foo', 'bar'], 'val': [4, 5]}).set_index('key')
left.join(right, lsuffix='_l', rsuffix='_r')
val_l val_r
key
foo 1 4
bar 2 5
The same functi...
git rebase without changing commit timestamps
...rresponding author dates, you can run:
git filter-branch --env-filter 'GIT_COMMITTER_DATE=$GIT_AUTHOR_DATE; export GIT_COMMITTER_DATE'
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How to check if a python module exists without importing it
...mport can find something in python2, using imp
import imp
try:
imp.find_module('eggs')
found = True
except ImportError:
found = False
To find dotted imports, you need to do more:
import imp
try:
spam_info = imp.find_module('spam')
spam = imp.load_module('spam', *spam_info)
i...
What's the difference between dynamic (C# 4) and var?
... {
[CompilerGenerated]
private static class <Main>o__SiteContainer0
{
public static CallSite<Action<CallSite, object>> <>p__Site1;
}
private static void Main(string[] args)
{
Junk a = new Junk(); /...
Is there a foreach loop in Go?
...
https://golang.org/ref/spec#For_range
A "for" statement with a "range" clause iterates through all entries
of an array, slice, string or map, or values received on a channel.
For each entry it assigns iteration values to corresponding iteration
v...
Linux 进程卡住了怎么办？ - 操作系统(内核) - 清泛网 - 专注C/C++及内核技术
...发现 ls 卡住了。
通过下面的命令可以看到 ls 卡在了 vfs_fstatat 调用上，它会给 FUSE 设备发送 getattr 请求，在等待回应。而 JuiceFS 客户端进程已经被我们停掉了，所以它就卡住了：
$ cat /proc/`pgrep ls`/stack
[<ffffffff813277c7>] request_w...
What is a singleton in C#?
...Prevent outside instantiation
}
private static readonly Singleton _singleton = new Singleton();
public static Singleton GetSingleton()
{
return _singleton;
}
}
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Do I need to disable NSLog before release Application?
...Debug configuration add a value to "Preprocessor Macros" value like:
DEBUG_MODE=1
Make sure you only do this for the Debug configuration and not for Beta or Release versions. Then in a common header file you can do something like:
#ifdef DEBUG_MODE
#define DLog( s, ... ) NSLog( @"<%p %@:(%d)&...