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I have the below code that returns the number of instances of an item in an array as a hash. I now need to check if the value is the same. For example if the hash is like this = {1=>3, 2=>3} i need to check if the value is the same, in this case it is but dont know how to check this.
arr.inject(Hash.new(0)) {|number,index| number[index] += 1 ;number}
Thanks
So, given h = { 1 => 3, 2 => 3 }, if I got you, you want to know if the values are ALL the same. If you knew the keys you could do
all_the_same = h[1] == h[2]
If there are more keys you want to check
all_the_same = h.values_at(1, 2, 3, 4).uniq.length == 1
If you don't know how many keys you have or which are these keys you could do
all_the_same = h.values.uniq.length == 1
Is it possible to initialize a list on one line in Dart? Something like the following...
List<int> options = new List<int>{ 1,2,5,9 };
(this is possible in c# and is called a collection initializer)
Yes:
List<int> options = [1, 2, 5, 9];
I'd recommend reading:
https://api.dartlang.org/stable/1.24.3/dart-core/List-class.html
Yes, you can do it using the List.unmodifiable constructor:
var options = new List.unmodifiable([3,6,7,8]);
Or by using the List.from constructor:
var options = new List.from([3,6,7,8]);
Or just like this:
var options = [5,7,9,0];
There are also available List.filled and List.generate factory constructors:
List<int?> s = List.filled(5, 10, growable: true); // [10, 10, 10, 10, 10]
This creates list of length 5, of type int or null, and initializes each element with 10. This list is growable, which means its length can be changed with a setter:
s.length = 10;
s[8] = 2; // [10, 10, 10, 10, 10, null, null, null, 2, null]
After changing the list length, new elements will be initialized with null. If the list element type is not-nullable this will cause Exception.
List.generate generates a list of values.
var n = List.generate(5, (index) => 0); // [0, 0, 0, 0, 0]
The created list is fixed-length, and each element is set to 0.
List<int?> n = List.generate(5, (index) => index * index, growable: true); // // [0, 1, 4, 9, 16]
If we want to create growable list (i.e. we set growable to true) we need to explicitly choose non-nullable type eg. int? as we did here, otherwise increasing list length will raise exception. This stands for both List.generate and List.filled factories.
Good reads about those are:
https://api.dart.dev/stable/1.24.3/dart-core/List/List.generate.html
and
https://api.dart.dev/stable/1.24.3/dart-core/List/List.filled.html
var vals = <int>[1, 2, 3];
var vals2 = List<int>()..addAll([1, 2, 3]);
var vals3 = List<int>.of([1, 2, 3]);
Note that when we don't provide a type, we in fact create a list of a
dynamic type. Also, the new keyword is optional.
Square brackets define a List
var listOfInt = [1,2,3]
Curly brackets define a Set
var setOfInt = {1,2,3};
Curly brackets with colons define a Map
var mapOfIntString = {1: "a", 2: "b"};
It is possible to specify the type explicitly.
var list = <int>[1,2,3]
var setOfInt = <int>{1,2,3};`
var map = <int,String>{1: "a", 2: "b"};
Initialize empty list
List<int> options = [];
Initialize filled list
List<int> options = [1,2,5,9];
I'm using Ruby on Rails 5.0.1 with Ruby 2.4. I have an array of objects, stored in the array, "results." Each object has a numeric attribute
numeric_attr
I would like to know, given my array, how I can tell if I have exactly one object with a numeric attribute value of "1" and incrementing by one. Order is not important. So, for instance, if I have an array of three objects,
[MyObject(numeric_attr = 2), MyObject(numeric_attr = 1), MyObject(numeric_attr = 3)]
I want to know if I have exactly one object with numeric_attr = 1, another object with numeric_attr = 2, and another with numeric_attr = 3. So the above satisfies the condition. The below example does not
[MyObject(numeric_attr = 4), MyObject(numeric_attr = 1), MyObject(numeric_attr = 3)]
because although there is an object with numeric_attr = 1, there is no object with numeric_attr = 2. It is possible thet the numeric_attr field is nil. How can I figure this out?
This one-liner should work:
results.map(&:numeric_attr).sort == (1..results.count).to_a
Explanation:
results
#=> [#<MyObject:... #attr=2>, #<MyObject:... #attr=3>, #<MyObject:... #attr=1>]
results.map(&:attr)
#=> [2, 3, 1]
results.map(&:attr).sort
#=> [1, 2, 3]
(1..results.length).to_a
#=> [1, 2, 3]
# therefore:
results.map(&:attr).sort == (1..results.count).to_a
#=> true
If there is a chance that numeric_attr is nil:
results.map(&:attr).compact.sort == (1..results.count).to_a
Of course, if there is even a single nil value, the result is guaranteed to be false.
If the sequence could start at any number, not just 1:
results.map(&:attr).sort == results.count.times.to_a.
map { |i| i + results.map(&:attr).sort.first }
This is not very efficient though, as it sorts the numbers twice.
If they always start at 1 #Máté's solution works, if they can start at any arbitrary number then you could:
count = 0
array_objects.sort_by(&:numeric_attr).each_cons(2) {|a,b| count+=1 if a.numeric_attr==b.numeric_attr-1 }
count+1==array_objects.count
Not as elegant but handles a lot more situations
There is an array like this:
a = [1,2,3,4]
I want to get the return values of size and sum like this.
size = a.size
sum = a.sum
Is there a way to get both values by a one-liner like this?
size, sum = a.some_method(&:size, &:sum)
In Ruby, you can do multiple assignments in one line:
size, sum = a.size, a.sum
It doesn't make it more readable, though.
You could do this:
a = [1,2,3,4]
methods = [:size, :max, :min, :first, :last]
methods.map { |m| a.send m }
#=> [4, 4, 1, 1, 4]
Another possible solution:
size, sum = a.size, a.reduce { |a,b| a = a + b }
Previous answers are correct, but if OP was actually concerned about walking the array multiple times, then array.size does not walk the array, it merely returns the length, thus there is no saving from a oneliner in that regard.
On the other hand, if size was just an example and the question is more about making multiple operations on an array in one go, then try something like this:
arr = [1,2,3,4,5,6]
product,sum = arr.inject([1,0]){|sums,el| [sums[0]*el, sums[1]+el]}
# => [720, 21]
That is, inject the array with multiple initial values for the results and then calculate new value for every element.
I have one scenario to sort the values based domain class property. This property may acept all numeric and alphanumeric values in the format XXX-1.
def res= Book.listOrderByName()
or
def res = Book.findAll("from Book order by name")
Giving the same result and result is displaying first numbers latter alphanumeric values.
My problem is :
these values are sorted before -.
for example i have AB-1,AB-2,...AB-12.
The result is displayed as AB-1,AB-10.AB-11,AB-2,AB-3,..AB-9
I have result like:
[18001,18002,2,300,3901,42,9,AB-1,AB-10,AB-2,AB-21,AB-9]
It should display the value as:
[2,9,42,300,3901,18001,18002,AB-1,AB-2,AB-9,AB-10,AB-21]
Run this in the Groovy console:
List sort(list) {
list.sort {a, b ->
a.class == b.class ? a <=> b : a instanceof Integer ? -1 : 1
}
}
// Test the sort function
def list = [18001,18002,2,300,3901,42,9,'AB-1','AB-10','AB-2','AB-21','AB-9']
assert sort(list) == [2, 9, 42, 300, 3901, 18001, 18002, 'AB-1', 'AB-10', 'AB-2', 'AB-21', 'AB-9']