Set literals were not supported until 2.2, How to set literals after Dart 2.2. Please feel free to comment. Thank you.
class item_t {
String name;
int weight;
int value;
}
main() {
const List<item_t> items = [
{'map', 9, 1}, // reports errors
];
}
update 1
I could define the list as a serial of define statements. However, it seems it is ineffective.
class item_t {
String name;
int weight;
int value;
}
main() {
// final item_t items = new item_t(100);
List<item_t> items = new List(2);
items[0].name = 'map';
items[0].weight = 9;
items[0].value = 1;
}
In C language, I can define a structure effectively but I don't know how to do that in dart.
typedef struct {
char *name;
int weight;
int value;
} item_t;
item_t items[] = {
{"map", 9, 150},
{"compass", 13, 35},
{"water", 153, 200},
};
update 2
Thank you jamesdlin's advise, I can simplify the list initialization and access the element by index. However, it still can't be as effective as C language.
var mySet = [
{"map", 9, 150},
{"compass", 13, 35},
{"water", 153, 200},
{"sandwich", 50, 160},
{"glucose", 15, 60},
{"tin", 68, 45},
{"banana", 27, 60},
{"apple", 39, 40},
{"cheese", 23, 30},
{"beer", 52, 10},
{"suntan cream", 11, 70},
{"camera", 32, 30},
{"T-shirt", 24, 15},
{"trousers", 48, 10},
{"umbrella", 73, 40},
{"waterproof trousers", 42, 70},
{"waterproof overclothes", 43, 75},
{"note-case", 22, 80},
{"sunglasses", 7, 20},
{"towel", 18, 12},
{"socks", 4, 50},
{"book", 30, 10}
];
print(mySet[0].elementAt(1));
You use { and } to specify Set (and Map) literals:
var mySet = {1, 2, 3};
Note that to avoid ambiguity with Map literals, you must explicitly specify a type when creating an empty set. For example:
var emptySet = <int>{};
Also see https://dart.dev/guides/language/language-tour#sets
Just replace { and } with [ and ], respectively, and everything will work fine.
Related
I have this simple code that doesn't compile.
const s = [_][_]int {
[_]int{08, 02, 22, 97, 38, 15, 00},
[_]int{49, 49, 99, 40, 17, 81, 18},
[_]int{81, 49, 31, 73, 55, 79, 14},
[_]int{52, 70, 95, 23, 04, 60, 11},
[_]int{22, 31, 16, 71, 51, 67, 63},
[_]int{24, 47, 32, 60, 99, 03, 45},
[_]int{32, 98, 81, 28, 64, 23, 67},
[_]int{67, 26, 20, 68, 02, 62, 12},
[_]int{24, 55, 58, 05, 66, 73, 99},
[_]int{21, 36, 23, 09, 75, 00, 76}
};
pub fn main() void
{
const w = s[0].len;
const h = s.len;
}
The compiler says:
./a.zig:1:14: error: inferred array size invalid here
const s = [_][_]int {
^
./a.zig:16:15: note: referenced here
const w = s[0].len;
What is the problem?
I'd be interested to know there's a deeper reason, but my simple understanding is that the current syntax [N]T allows for the array size to be elided using _, but not for more than one dimension.
So you can fix your problem using the following (N.B. I've used u8 because I'm unsure what your int is):
const s = [_][7]u8{
// Your items
}
I suspect this is because of the way the parsing rules are applied, so [7]u8 would be the type your nested array would hold, and will be used by the compiler to check contents are all of type [7]u8; you can confirm this by modifying one of your rows to have 6 elements and examining the resulting error.
If you want a variable number of items, you could start to look into an array of slices: [_][]u8, but I don't think that's what you're currently after.
Imagine this array of timestamps [Double] :
hourlyTimes": [1551344400, 1551348000, 1551351600, 1551355200, 1551358800, 1551362400, 1551366000, 1551369600, 1551373200 ... ]
It corresponds to the hours for which I have data to display.
To keep it simple, here is the full array when I display only the hours (UTC) :
Hours = [9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 0, 3, 6, 9, 12, 15, 18, 21, 0, 3, 6, 9, 12, 15, 18, 0, 6, 12, 18, 0, 6, 12, 18, 0, 6, 12, 18, 0, 6, 12, 18, 0, 6, 12, 18, 0]
Now here is what I want to achieve, I need to filter this array of timestamp, in order to only keep these specific hours on any day (three-hourly).
[0, 3, 6, 9, 12, 15, 18, 21]
Ok, now let's have a look at the code :
let arrayOfTimestamp = time.hourlyTimes
let arrayOfHours = arrayOfTimestamp.map({ Date.init(timeIntervalSince1970: $0).hoursUTC})
let hoursToKeep = [0, 3, 6, 9, 12, 15, 18, 21]
let filtered = arrayOfHours.intersection(with: hoursToKeep)
Some explanations here:
time in the first line is the response from the backend, returning me all the available timestamps.
struct MultiForecastTimeModel: Codable {
let hourlyTimes: [Double]
let dailyTimes: [Double]
}
.hoursUTC is just a Date extension, in order to retrieve the hour component of the Date object.
var hoursUTC: Int {
var calendar = Calendar.current
let timezone = TimeZone(abbreviation: "UTC")!
calendar.timeZone = timezone
return calendar.component(.hour, from: self)
}
And finally, .intersection is an extension too, in order to do the same as a classic intersection, but also keeping the index and the occurrences.
extension Collection where Element: Equatable {
func intersection(with filter: [Element]) -> [Element] {
return self.filter { element in filter.contains(element) }
}
}
Everything is working fine, my only issue is that I now have to associate all these values as an Array of tuples.
Like this :
let tuples = Array(zip(filtered, filtered.dropFirst()))
But with an actual timestamp (corresponding to real date), not just an array of Int (hour component).
Because in the end, here what I have to do :
self.hourlyMapDataSource.data.value = tuples
and my datasource is expecting a tuple of timestamp (Double, Double)
class HourlyMapDataSource : GenericDataSource<(Double, Double)>, UICollectionViewDataSource { }
Do you have any pieces of advice on how should I improve my code and/or my logic?
Thank you in advance.
EDIT: My tuple array should only contain timestamps whose time has been "validated" through the hoursToKeep array so that it has 3 hours difference between hours.
I will show you with the hours to keep it simple, but it's an actual corresponding timestamp that I want :
[(9, 12), (12, 15), (15, 18) ...]
var tupleArray = hourlyTimes.map { (time: $0, hour: Date.init(timeIntervalSince1970: $0).hoursUTC)}
Now you can run the reduce function on this
var selectedHours = tupleArray.filter { return hoursToKeep.contains($0.hour) }
This will give you an array of tuples which have the validated hours,
[(1551344400, 9), (1551348000, 12)]
I set up an array like this:
let modelArray = [
"Casual": ["health": 17, "weapon": 8, "crafting": 15, "social": 30],
"Soldier": ["health": 25, "weapon": 32, "crafting": 8, "social": 5],
"Doctor": ["health": 35, "weapon": 5, "crafting": 15, "social": 15],
"Dorothy": ["health": 15, "weapon": 15, "crafting": 20, "social": 20],
"Asian": ["health": 13, "weapon": 5, "crafting": 7, "social": 45],
"Police": ["health": 23, "weapon": 22, "crafting": 5, "social": 20]
]
How do I access the String (for example "Casual") value when looping?
for (index, model) in character.modelArray.enumerate()
{
print("\(index) carries: \(model[0]")
}
This gives me Type '(String, Dictionary)' has no subscript members
As Josh points out, your modelArray object is a dictionary of dictionaries. (let modelArray : [String: [String:Int]] is the full type information).
The dictionary within can't be subscripted using an Int, only a String.
Here's a version of your code, which will get some the health stat of each character:
for statDictionary in characters.modelArray {
let health = statDictionary["health"]
print(health)
}
further suggestion
Storing data like this in a dictionary is fine for some purposes, but you may find a cleaner, safer API can be made by creating structs (or classes) for holding this state information.
struct CharacterStats {
let health : Int
let weaponNumber : Int
// etc.
}
Then enumerating would be even simpler and require no loose string keys (which could be mistyped).
for stat in characters {
let health = stat.health
}
Just my point of view.
A dictionary of dictionaries is ugly
Create a model type
struct Model {
let name: String
let health: Int
let weapon: Int
let crafting: Int
let social: Int
}
and then your array
let models = [
Model(name: "Casual", health: 17, weapon: 8, crafting: 15, social: 30),
Model(name: "Soldier", health: 25, weapon: 32, crafting: 8, social: 5),
Model(name: "Doctor", health: 35, weapon: 5, crafting: 15, social: 15),
Model(name: "Dorothy", health: 15, weapon: 15, crafting: 20, social: 20),
Model(name: "Asian", health: 13, weapon: 5, crafting: 7, social: 45),
Model(name: "Police", health: 23, weapon: 22, crafting: 5, social: 20),
]
Looping
Now you can simply
for model in models {
print(model.name)
}
Update: Searching
if let doctor = models.filter({ $0.name == "Doctor" }).first {
print(doctor.health)
}
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] */
I'm trying to work out an example which is provided on developer.apple.com website 'Swift Playground'. I had to adapt it a little since swift 2 is, what looks like, different in handling 'inout' variables. In the example showed on the presentation 'inout' was not used in the function declaration. Anyway the result of 'data' is not showing in the Playground although the code doesn't show any compile errors.
import UIKit
var data = [16, 97, 13, 55, 95, 53, 18, 10, 79, 53, 79, 34, 50, 34, 0, 91, 94, 55, 6, 38, 7]
func exchange<T>(inout data:[T], i: Int, j: Int) {
let temp = data[i]
data[i] = data[j]
data[j] = temp
}
func swapLeft<T: Comparable>(inout data: [T], index: Int) {
for i in reverse(1...index) {
if data[i] < data[i-1] {
exchange(&data, i, i-1)
}else {
break
}
}
}
func isort<T: Comparable>(inout data: [T]) {
for i in 1...data.count {
swapLeft(&data,i)
}
}
data //result [16, 97, 13, 55, 95, 53, 18, 10, 79, 53, 79, 34, 50, 34, 0, 91, 94, 55, 6, 38, 7]
isort(&data)
data //no result shown
Screenshot
It isn't showing a result because it is crashing with Array index out of range. Try this for isort:
func isort<T: Comparable>(inout data: [T]) {
for i in 1..<data.count {
swapLeft(&data,i)
}
}
You can always use println(data)
Make sure your Debug Area is shown. See this post for more info.