Get last 10 elements from array : NSMakeRange [duplicate] - ios

This question already has answers here:
In Swift, what's the cleanest way to get the last two items in an Array?
(9 answers)
Closed 5 years ago.
I need to get last 10 elements or min of 10 and array.count. In objective-C I have done it like this :
Objective-C code :
NSRange endRange = NSMakeRange(sortedArray.count >= 10 ? sortedArray.count - 10 : 0, MIN(sortedArray.count, 10));
NSArray *lastElements= [sortedArray subarrayWithRange:endRange];
In Swift I have done this :
let endRange = NSMakeRange(values.count >= 10 ? values.count - 10 : 0, min(values.count , 10) )
But don't know how to get the array using this range in swift. Any help would be appreciated. Thanks.

You can use Array Instance Method suffix(_:). Note that using suffix you don't need to check your array count. It will take up to 10 elements from the end of your array.
let array = Array(1...100) // [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100]
let lastTenElements = Array(array.suffix(10)) // [91, 92, 93, 94, 95, 96, 97, 98, 99, 100]

You can get it by declaring Range:
let letters = ["a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n"]
let desiredRange = letters.index(letters.endIndex, offsetBy: -10) ..< letters.endIndex
// ["e", "f", "g", "h", "i", "j", "k", "l", "m", "n"]
let lastTenLetters = (desiredRange.count > letters.count) ? letters : Array(letters[desiredRange])
Note that if the desired range's count is more than the main array's count, the last ten elements should be the whole main array.
Although I still agree that Leo's answer is the proper one for your case, I would like to mention that the good thing about this solution is that it is applicable for not only last element, to make it clear, consider that you want to get 10 elements after the first one (referring to letters array, elements should be b-k), by implementing a desired range, you could achieve this, as follows:
let letters = ["a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n"]
let desiredRange = letters.index(letters.startIndex, offsetBy: 1) ..< letters.index(letters.startIndex, offsetBy: 11)
// ["b", "c", "d", "e", "f", "g", "h", "i", "j", "k"]
let lastTenLetters = (desiredRange.count > letters.count) ? letters : Array(letters[desiredRange])

var values : NSArray = [1,2,3,4,5,6,7,8,9,10,11]
values = values.reversed() as NSArray
let tenDigits = values.prefix(10)
debugPrint(values.count >= 10 ? NSArray(array: (Array(tenDigits))) : min(values.count , 10))

Related

Implementing WeightedRandomSampler on imbalanced data set: RuntimeError: invalid multinomial distribution

I am trying to implement a weighted sampler for a very imbalanced data set. There are 182 different classes. Here is an array of the bin counts per class:
array([69487, 5770, 5753, 138, 4308, 10, 1161, 29, 5611,
350, 7, 183, 218, 4, 3, 3872, 5, 950,
33, 3, 443, 16, 20, 330, 4353, 186, 19,
122, 546, 6, 44, 6, 3561, 2186, 3, 48,
8440, 338, 9, 610, 74, 236, 160, 449, 72,
6, 37, 1729, 2255, 1392, 12, 1, 3426, 513,
44, 3, 28, 12, 9, 27, 5, 75, 15,
3, 21, 549, 7, 25, 871, 240, 128, 28,
253, 62, 55, 12, 8, 57, 16, 99, 6,
5, 150, 7, 110, 8, 2, 1296, 70, 1927,
470, 1, 1, 511, 2, 620, 946, 36, 19,
21, 39, 6, 101, 15, 7, 1, 90, 29,
40, 14, 1, 4, 330, 1099, 1248, 1146, 7414,
934, 156, 80, 755, 3, 6, 6, 9, 21,
70, 219, 3, 3, 15, 15, 12, 69, 21,
15, 3, 101, 9, 9, 11, 6, 32, 6,
32, 4422, 16282, 12408, 2959, 3352, 146, 1329, 1300,
3795, 90, 1109, 120, 48, 23, 9, 1, 6,
2, 1, 11, 5, 27, 3, 7, 1, 3,
70, 1598, 254, 90, 20, 120, 380, 230, 180,
10, 10])
In some classes, instances are as low as 1. I am trying to implement a Weighted random sampler from torch for this dataset. However, as the class imbalance is so large, when I calculate weights using
count_occr = np.bincount(dataset.y)
lbl_weights = 1. / count_occr
weights = np.array(lbl_weights)
weights = torch.from_numpy(weights)
sampler = WeightedRandomSampler(weights.type('torch.DoubleTensor'), len(weights*2))
I get two error messages:
RuntimeWarning: divide by zero encountered in true_divide
and
RuntimeError: invalid multinomial distribution (encountering probability entry = infinity or NaN)
Does anyone have a work around for this ? I was considering multiplying the lbl_weights by some scalar however I am not sure if this is a viable option.

Dart Bech32 and Hex encoding and decoding

I'm trying to decode this Bech32 address into a hex.
When given cosmos1qpjrq625nglf3xx9chdkq953nhrd3nygte44rt. It breaks it down into it's head which is 'cosmos' and the remainder is represented as a List of 8-bit unsigned integers (Uint8List).
When this is encoded to hexadecimal (HEX.Encode), i get a value of 00011203001a0a1413081f091106060518170d16000514111317030d11130408.
However, it is meant to be getting me 00643069549a3e9898c5c5db6016919dc6d8cc88 instead.
You can check this if you go to https://slowli.github.io/bech32-buffer/ -> and decode cosmos1qpjrq625nglf3xx9chdkq953nhrd3nygte44rt which gives 00643069549a3e9898c5c5db6016919dc6d8cc88.
I can't figure out the issue, is it perhaps
-The formatting is wrong, different bases? or am i doing this completely wrong.
Thanks and i appreciate any replies
Here is a snippet of code;
import 'package:bech32/bech32.dart';
import 'package:hex/hex.dart';
Bech32Codec bech32codec = Bech32Codec();
// target address : 00643069549a3e9898c5c5db6016919dc6d8cc88 -> to get to this address
String address = 'cosmos1qpjrq625nglf3xx9chdkq953nhrd3nygte44rt';
Bech32 bech32 = bech32codec.decode(address);
print(bech32.data);
// this returns [0, 1, 18, 3, 0, 26, 10, 20, 19, 8, 31, 9, 17, 6, 6, 5, 24, 23, 13, 22, 0, 5, 20, 17, 19, 23, 3, 13, 17, 19, 4, 8]
print(bech32.hrp);
print(bech32codec.encode(Bech32("cosmos", bech32.data)));
var answer2 = HEX.encode(bech32.data);
print(answer2);
var decode = HEX.decode('00643069549a3e9898c5c5db6016919dc6d8cc88');
print(decode);
// this returns [0, 100, 48, 105, 84, 154, 62, 152, 152, 197, 197, 219, 96, 22, 145, 157, 198, 216, 204, 136]

How to create array from 1 to n digit with single line of code in ruby [duplicate]

This question already has answers here:
Create array of n items based on integer value
(6 answers)
Closed 4 years ago.
Need to create an array of 1 to n numbers with a single line of code in ruby.
I have tried it using while loop. But I'm sure there are other simpler way of doing this in ruby.
a = []
b = 1
while b < 100 do
a << b
b += 1
end
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99]
Convert a range into an array.
(1..n).to_a
another way
You can just splat a range:
[*1..n]
example
[*1..10]
=>[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
Or
a= Array(0..10)
puts a # => =>[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

Use UISlider to get integer value in range

I'm trying to solve this issue in the most accurate way.
I have a UISlider, and a range between 0 to 300 (All primes).
How can I, using the UISlider, get an accurate access to each prime number in this range, while moving the slider? Any thoughts?
Store the first 0-300 prime numbers in an array
Bad way of doing it.
Set slider min to 0, and max to 300, and current to 0
When moving the slider check if the slider number exists in the array, if it does, update the label's text with the prime number
let primes = [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199, 211, 223, 227, 229, 233, 239, 241, 251, 257, 263, 269, 271, 277, 281, 283, 293]
#IBOutlet weak var label: UILabel!
#IBAction func slider(sender: UISlider) {
let sliderNumber = Int(sender.value)
if primes.contains(sliderNumber) {
label.text = "\(sliderNumber)"
}
}
Good way to do it.
Set slider min to 0, and max to 61, and current to 0.
There are 62 prime numbers in the first 0-300.
When moving the slider, change the label text by indexing the primes array.
let primes = [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199, 211, 223, 227, 229, 233, 239, 241, 251, 257, 263, 269, 271, 277, 281, 283, 293]
#IBOutlet weak var label: UILabel!
#IBAction func slider(sender: UISlider) {
let sliderNumber = Int(sender.value)
label.text = String(primes[sliderNumber])
}
Tested both the first and this second implementation, and the second one is much cleaner on the value transition.

Swift converting signed array of Int [int8] to unsigned array of Int [UInt8]

How to convert signed array of [Int8] to unsigned array of [UInt8].
let arryData: [Int8] = [-108, 11, -107, -14, 35, -57, -116, 118, 54, 91, 12, 67, 21, 29, -44, 111]
I just want to convert this above into array of Unsigned [UInt8]. How to achieve this in swift.? Thanks in advance.
If your intention is to convert signed 8-bit integers to
unsigned ones with the same bit representation (e.g. -1 -> 255):
let intArray: [Int8] = [0, 1, 2, 127, -1, -2, -128]
let uintArray = intArray.map { UInt8(bitPattern: $0) }
print(uintArray)
// [0, 1, 2, 127, 255, 254, 128]
[Int8] -> [UInt8]
You haven't specified how you want to treat negative values; by flipping them to their positive counterpart or by removing them. Below follows both cases.
Transforming negative values to positive ones by flipping sign:
let arrayData: [Int8] = [-108, 11, -107, -14, 35, -57, -116, 118, 54, 91, 12, 67, 21, 29, -44, 111]
let arrayDataUnsigned = arrayData.map { UInt8(abs($0)) }
/* [108, 11, 107, 14, 35, 57, 116, 118, 54, 91,
12, 67, 21, 29, 44, 111] */
Or, by removing the negative values:
let arrayDataUnsigned = arrayData.flatMap { $0 < 0 ? nil : UInt8($0) }
/* [11, 35, 118, 54, 91, 12, 67, 21, 29, 111] */

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