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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>...
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...
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 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)&...
What are the differences between type() and isinstance()?
...caters for inheritance (an instance of a derived class is an instance of a base class, too), while checking for equality of type does not (it demands identity of types and rejects instances of subtypes, AKA subclasses).
Normally, in Python, you want your code to support inheritance, of course (sinc...
How can I maintain fragment state when added to the back stack?
...sion 1. Use version 2)
public class FragmentA extends Fragment {
View _rootView;
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
if (_rootView == null) {
// Inflate the layout for this fragment
_...
Generating all permutations of a given string
... all the permutations of the remaining letters using a recursive call.
The base case is when the input is an empty string the only permutation is the empty string.
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How to determine whether code is running in DEBUG / RELEASE build?
...n though. You may see DEBUG changed to another variable name such as DEBUG_MODE.
then conditionally code for DEBUG in your source files
#ifdef DEBUG
// Something to log your sensitive data here
#else
//
#endif
sha...
How to wait for several Futures?
...]):Future[List[Any]] = {
val fut = if (futures.size == 1) futures.head._2
else Future.firstCompletedOf(futures.values)
fut onComplete{
case Success(value) if (futures.size == 1)=>
prom.success(value :: values)
case Success(value) =>
processFutures(fut...