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How do you delete a column by name in data.table?
To get rid of a column named "foo" in a data.frame , I can do:
8 Answers
8
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How do I find out which keystore was used to sign an app?
I have an app which is signed and several keystore files. I'd like to update the app, so I need to find out which one of keys was used.
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From an array of objects, extract value of a property as array
...ere is a shorter way of achieving it:
let result = objArray.map(a => a.foo);
OR
let result = objArray.map(({ foo }) => foo)
You can also check Array.prototype.map().
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PowerShell: Setting an environment variable for a single command only
...ariable. But if that is what you need to do you can do it this way:
$env:FOO = 'BAR'; ./myscript
The environment variable $env:FOO can be deleted later like so:
Remove-Item Env:\FOO
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URL rewriting with PHP
I have a URL that looks like:
5 Answers
5
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What are static factory methods?
... a factory method, you would simply call the class's constructor directly: Foo x = new Foo(). With this pattern, you would instead call the factory method: Foo x = Foo.create(). The constructors are marked private, so they cannot be called except from inside the class, and the factory method is m...
Explicitly calling a default method in Java
...s per this article you access default method in interface A using
A.super.foo();
This could be used as follows (assuming interfaces A and C both have default methods foo())
public class ChildClass implements A, C {
@Override
public void foo() {
//you could completely override ...
How to pass a single object[] to a params object[]
...imple typecast will ensure the compiler knows what you mean in this case.
Foo((object)new object[]{ (object)"1", (object)"2" }));
As an array is a subtype of object, this all works out. Bit of an odd solution though, I'll agree.
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How to make a class property? [duplicate]
... bar(cls, value):
cls._bar = value
# test instance instantiation
foo = Bar()
assert foo.bar == 1
baz = Bar()
assert baz.bar == 1
# test static variable
baz.bar = 5
assert foo.bar == 5
# test setting variable on the class
Bar.bar = 50
assert baz.bar == 50
assert foo.bar == 50
The sette...
Number of lines in a file in Java
I use huge data files, sometimes I only need to know the number of lines in these files, usually I open them up and read them line by line until I reach the end of the file
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