What is the meaning of [] in a matlab function argument?
[]
is an empty matrix. In many MATLAB built-in functions, an empty matrix is interpreted to mean "use the default argument here" or "automatically determine this value". Occasionally it is used to disambiguate two meanings of a function, as with the max
function, where max(A,2)
compares each element of A
to 2 and returns the larger, while max(A,[],2)
finds the largest element of each row.
If you read the help for reshape
, you will see the following:
You can specify a single dimension size of
[]
to have the dimension size automatically calculated, such that the number of elements inB
matches the number of elements inA
. For example, ifA
is a 10-by-10 matrix, thenreshape(A,2,2,[])
reshapes the 100 elements ofA
into a 2-by-2-by-25 array.
What does this symbol mean in JavaScript?
See the documentation on MDN about expressions and operators and statements.
Basic keywords and general expressions
this
keyword:
- How does the "this" keyword work?
var x = function()
vs. function x()
— Function declaration syntax
- var functionName = function() {} vs function functionName() {}
(function(){
…})()
— IIFE (Immediately Invoked Function Expression)
- What is the purpose?, How is it called?
- Why does
(function(){…})();
work butfunction(){…}();
doesn't? (function(){…})();
vs(function(){…}());
- shorter alternatives:
!function(){…}();
- What does the exclamation mark do before the function?+function(){…}();
- JavaScript plus sign in front of function expression- !function(){ }() vs (function(){ })(),
!
vs leading semicolon
(function(window, undefined){…}(window));
someFunction()()
— Functions which return other functions
- Two sets of parentheses after function call
=>
— Equal sign, greater than: arrow function expression syntax
- What's the meaning of "=>" (an arrow formed from equals & greater than) in JavaScript?
|>
— Pipe, greater than: Pipeline operator
- What does the "|>" operator do in JavaScript?
function*
, yield
, yield*
— Star after function
or yield
: generator functions
- What is "function*" in JavaScript?
- What's the yield keyword in JavaScript?
- Delegated yield (yield star, yield *) in generator functions
[]
, Array()
— Square brackets: array notation
- What’s the difference between "Array()" and "[]" while declaring a JavaScript array?
- What is array literal notation in javascript and when should you use it?
If the square brackets appear on the left side of an assignment ([a] = ...
), or inside a function's parameters, it's a destructuring assignment.
{key: value}
— Curly brackets: object literal syntax (not to be confused with blocks)
- What do curly braces in JavaScript mean?
- Javascript object literal: what exactly is {a, b, c}?
- What do square brackets around a property name in an object literal mean?
- How does this object method definition work without the "function" keyword? (ES2015 Method definitions)
If the curly brackets appear on the left side of an assignment ({ a } = ...
) or inside a function's parameters, it's a destructuring assignment.
`
…${
…}
…`
— Backticks, dollar sign with curly brackets: template literals
- What does this
`…${…}…`
code from the node docs mean? - Usage of the backtick character (`) in JavaScript?
- What is the purpose of template literals (backticks) following a function in ES6?
/
…/
— Slashes: regular expression literals
- Meaning of javascript text between two slashes
$
— Dollar sign in regex replace patterns: $$
, $&
, $`
, $'
, $n
- JavaScript replace() method dollar signs
()
— Parentheses: grouping operator
- MDN: Grouping operator
Property-related expressions
obj.prop
, obj[prop]
, obj["prop"]
— Square brackets or dot: property accessors
- JavaScript property access: dot notation vs. brackets?
?.
, ?.[]
, ?.()
— Question mark, dot: optional chaining operator
- Question mark after parameter
- Null-safe property access (and conditional assignment) in ES6/2015
- Optional Chaining in JavaScript
- Is there a null-coalescing (Elvis) operator or safe navigation operator in javascript?
- Is there a "null coalescing" operator in JavaScript?
::
— Double colon: bind operator
- JavaScript double colon (bind operator)
new
operator
- What is the 'new' keyword in JavaScript?
- What is "new.target"?
...iter
— Three dots: spread syntax; rest parameters
(...rest) => {}
— What is the meaning of “…args” (three dots) in a function definition?fn(...args)
— What is the meaning of “foo(…arg)” (three dots in a function call)?[...iter]
— javascript es6 array feature […data, 0] “spread operator”{...props}
— Javascript Property with three dots (…), What does the '…rest' stand for in this object destructuring?
Increment and decrement
++
, --
— Double plus or minus: pre- / post-increment / -decrement operators
++someVariable
vssomeVariable++
in Javascript
Unary and binary (arithmetic, logical, bitwise) operators
delete
operator
- What is the purpose of the delete operator in Javascript?
void
operator
- What does `void 0` mean?
+
, -
— Plus and minus: addition or concatenation, and subtraction operators; unary sign operators
- What does = +_ mean in JavaScript, Single plus operator in javascript
- What's the significant use of unary plus and minus operators?
- Why is [1,2] + [3,4] = "1,23,4" in JavaScript?
- Why does JavaScript handle the plus and minus operators between strings and numbers differently?
|
, &
, ^
, ~
— Single pipe, ampersand, circumflex, tilde: bitwise OR, AND, XOR, & NOT operators
- What do these JavaScript bitwise operators do?
- How to: The ~ operator?
- Is there a & logical operator in Javascript
- What does the "|" (single pipe) do in JavaScript?
- What does the operator |= do in JavaScript?
- What does the ^ (caret) symbol do in JavaScript?
- Using bitwise OR 0 to floor a number, How does x|0 floor the number in JavaScript?
- Why does
~1
equal-2
? - What does ~~ ("double tilde") do in Javascript?
- How does !!~ (not not tilde/bang bang tilde) alter the result of a 'contains/included' Array method call? (also here and here)
%
— Percent sign: remainder operator
- What does % do in JavaScript?
&&
, ||
, !
— Double ampersand, double pipe, exclamation point: logical operators
- Logical operators in JavaScript — how do you use them?
- Logical operator || in javascript, 0 stands for Boolean false?
- What does "var FOO = FOO || {}" (assign a variable or an empty object to that variable) mean in Javascript?, JavaScript OR (||) variable assignment explanation, What does the construct x = x || y mean?
- Javascript AND operator within assignment
- What is "x && foo()"? (also here and here)
- What is the !! (not not) operator in JavaScript?
- What is an exclamation point in JavaScript?
??
— Double question mark: nullish-coalescing operator
- How is the nullish coalescing operator (??) different from the logical OR operator (||) in ECMAScript?
- Is there a null-coalescing (Elvis) operator or safe navigation operator in javascript?
- Is there a "null coalescing" operator in JavaScript?
**
— Double star: power operator (exponentiation)
x ** 2
is equivalent toMath.pow(x, 2)
- Is the double asterisk ** a valid JavaScript operator?
- MDN documentation
Equality operators
==
, ===
— Equal signs: equality operators
- Which equals operator (== vs ===) should be used in JavaScript comparisons?
- How does JS type coercion work?
- In Javascript, <int-value> == "<int-value>" evaluates to true. Why is it so?
- [] == ![] evaluates to true
- Why does "undefined equals false" return false?
- Why does !new Boolean(false) equals false in JavaScript?
- Javascript 0 == '0'. Explain this example
- Why false == "false" is false?
!=
, !==
— Exclamation point and equal signs: inequality operators
- != vs. !==
- What is the difference between != and !== operators in JavaScript?
Bit shift operators
<<
, >>
, >>>
— Two or three angle brackets: bit shift operators
- What do these JavaScript bitwise operators do?
- Double more-than symbol in JavaScript
- What is the JavaScript >>> operator and how do you use it?
Conditional operator
…?
…:
… — Question mark and colon: conditional (ternary) operator
- Question mark and colon in JavaScript
- Operator precedence with Javascript Ternary operator
- How do you use the ? : (conditional) operator in JavaScript?
Assignment operators
=
— Equal sign: assignment operator
- What is the difference between the `=` and `==` operators and what is `===`? (Single, double, and triple equals)
This symbol is also used for default parameters or default values in a destructuring assignment:
- what does (state = {}) => state means
- What does ({"key": "value"} = {}) syntax mean inside a JavaScript function
%=
— Percent equals: remainder assignment
- Having Confusion with Modulo operator
+=
— Plus equals: addition assignment operator
- How does += (plus equal) work?
&&=
, ||=
, ??=
— Double ampersand, pipe, or question mark, followed by equal sign: logical assignments
- What purpose do &&=, ||= and ??= serve?
- Replace a value if null or undefined in JavaScript
- Set a variable if undefined
- Ruby’s
||=
(or equals) in JavaScript? - Original proposal
- Specification
<<=
, >>=
, >>>=
, &=
, ^=
, |=
— Double less than, double greater than, triple greater than, ampersand, caret, or pipe followed by equal sign: bitwise assignments
- What do these JavaScript bitwise operators do?
Destructuring
- of function parameters: Where can I get info on the object parameter syntax for JavaScript functions?
- of arrays: Multiple assignment in javascript? What does [a,b,c] = [1, 2, 3]; mean?
- of objects/imports: Javascript object bracket notation ({ Navigation } =) on left side of assign
Comma operator
,
— Comma operator (not to be confused with the comma used in variable declarations)
- What does a comma do in JavaScript expressions?
- Comma operator returns first value instead of second in argument list?
- When is the comma operator useful?
Control flow
{
…}
— Curly brackets: blocks (not to be confused with object literal syntax)
- JavaScript curly braces with no function or json
Declarations
var
, let
, const
— Declaring variables
- What's the difference between using "let" and "var"?
- Are there constants in JavaScript?
- What is the temporal dead zone?
var a, b;
— Comma used in variable declarations (not to be confused with the comma operator): JavaScript variable definition: Commas vs. Semicolons
Label
label:
— Colon: labels
- What does the JavaScript syntax foo: mean?
- What does ':' (colon) do in JavaScript?
Other
123n
— n
after integer: BigInt
- What does character 'n' after numeric literal mean in JavaScript?
#
— Hash (number sign): Private methods or private fields
- What does the
#
symbol do in JavaScript?
_
— Underscore: separator in numeric literals
- Javascript numeric separators?
- Is there a Javascript equivalent to the Ruby syntax using underscores (e.g. 10_000 = 10000) to make larger integers human readable?
What is the meaning of '*' and '&'?
This is possibly one of the most confusing things in Go. There are basically 3 cases you need to understand:
The &
Operator
&
goes in front of a variable when you want to get that variable's memory address.
The *
Operator
*
goes in front of a variable that holds a memory address and resolves it (it is therefore the counterpart to the &
operator). It goes and gets the thing that the pointer was pointing at, e.g. *myString
.
myString := "Hi"
fmt.Println(*&myString) // prints "Hi"
or more usefully, something like
myStructPointer = &myStruct
// ...
(*myStructPointer).someAttribute = "New Value"
*
in front of a Type
When *
is put in front of a type, e.g. *string
, it becomes part of the type declaration, so you can say "this variable holds a pointer to a string". For example:
var str_pointer *string
So the confusing thing is that the *
really gets used for 2 separate (albeit related) things. The star can be an operator or part of a type.
What is the meaning of [:] in python
[:]
is the array slice syntax for every element in the array.
This answer here goes more in depth of the general uses: Explain Python's slice notation
del arr # Deletes the array itself
del arr[:] # Deletes all the elements in the array
del arr[2] # Deletes the second element in the array
del arr[1:] # etc..
Python: What does the use of [] mean here?
[]
is an empty list.
[foo.bar]
is creating a new list ([]
) with foo.bar
as the first item in the list, which can then be referenced by its index:
var = [foo.bar]
var[0] == foo.bar # returns True
So your guess that your assignment of foo.bar = [1,2]
is exactly right.
If you haven't already, I recommend playing around with this kind of thing in the Python interactive interpreter. It makes it pretty easy:
>>> []
[]
>>> foobar = [1,2]
>>> foobar
[1, 2]
>>> [foobar]
[[1, 2]]
What is the meaning of square brackets on a function parameter
It's destructuring - the function takes an array as its argument and fileEntry
is the first entry of that array.
Simpler example (JavaScript):
const firstEl = ([el]) => el;
console.log(firstEl([a, b, c]));
What is the meaning of brackets in this code
Those are parentheses: ()
, not brackets: []
or braces: {}
, and this is called Casting. Here's some good documentation: Casting and Type Conversions.
In this case, it means that e.CurrentSelection.FirstOrDefault()
will be explicitly converted to an instance of TripLogEntry
(instead of just object
).
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