Get the First Element of an Array

Get the first element of an array

Original answer, but costly (O(n)):

array_shift(array_values($array));

In O(1):

array_pop(array_reverse($array));

Other use cases, etc...

If modifying (in the sense of resetting array pointers) of $array is not a problem, you might use:

reset($array);

This should be theoretically more efficient, if a array "copy" is needed:

array_shift(array_slice($array, 0, 1));

With PHP 5.4+ (but might cause an index error if empty):

array_values($array)[0];

How to get the first element of an array?

like this

alert(ary[0])

Get the first element of System.array?

IndexOf is for finding the index of the first element in the array that matches the value you passed. I think you're after [0].

String windowClass = BFS.Window.GetClass(myArray[0]);

Please note that if the array is empty this will throw an exception.

You could also use .First() or FirstOrDefault() from System.Linq, but [0] is made for what you need.

How to get the first element of a array?

I'm not familiar with pm2, but if the array is JSON-compatible (which it looks like it is), you can use jq, for example:

$ echo '[2]' | jq '.[0]'
2
$ echo '[3, 2]' | jq '.[0]'
3

Here's a related question with some other methods: get the first (or n'th) element in a jq json parsing

Get index from 2d array where first element is the index

One approach is to use next on a generator expression

lst = [[0, {'dt_name': 'Go'}], [1, {'dt_name': 'Stop'}]]
res = next(i for (i, t) in lst if t['dt_name'] == 'Go')
print(res)

Output

0

This approach avoids building any additional list.

Some timings on list vs generator:

lst = [[0, {'dt_name': 'Go'}], [1, {'dt_name': 'Stop'}]] * 100
%timeit next(i for (i, t) in lst if t['dt_name'] == 'Go')
452 ns ± 2.18 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)
%timeit [i for (i, t) in lst if t['dt_name'] == 'Go'][0]
12.1 µs ± 36.1 ns per loop (mean ± std. dev. of 7 runs, 100000 loops each)

In the above example using next on the generator is about 24 times faster.

Why does the first element outside of a defined array default to zero?

I'm a bit confused as to why that last element outside of the array
always "defaults" to zero.

In this declaration

int x[] = {120, 200, 16};

the array x has exactly three elements. So accessing memory outside the bounds of the array invokes undefined behavior.

That is, this loop

 for (int i = 0; i < 4; i++)
 cout << x[i] << " ";

invokes undefined behavior. The memory after the last element of the array can contain anything.

On the other hand, if the array were declared as

int x[4] = {120, 200, 16};

that is, with four elements, then the last element of the array that does not have an explicit initializer will be indeed initialized to zero.

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