Szathmáry László honlapja @ DEIK | DLang / Create a dictionary; read/write

Dictionaries in D are unordered collections.

(1) create a dictionary; read/write
def main(): # d: dict[int, str] = {} d = {} d[1] = "one" d[3] = "three" print(d) # {1: 'one', 3: 'three'} d2 = { 1: "one", 3: "three" } print(d2) # {1: 'one', 3: 'three'} # print a value print(d[1]) # one	import std.stdio; void main() { string[int] d; // order: value[key] d[1] = "one"; d[3] = "three"; writeln(d); // [3:"three", 1:"one"] auto d2 = [ 1: "one", 3: "three" ]; writeln(d2); // [3:"three", 1:"one"] // print a value writeln(d[1]); // one }
def main(): d = {} d[1] = ["one", "egy"] d[2] = ["two", "kettő"] d[3] = ["three", "három"] print(d) """ {1: ['one', 'egy'], 2: ['two', 'kettő'], 3: ['three', 'három']} """	import std.stdio; void main() { string[][int] d; d[1] = ["one", "egy"]; d[2] = ["two", "kettő"]; d[3] = ["three", "három"]; writeln(d); /* [3:["three", "három"], 2:["two", "kettő"], 1:["one", "egy"]] */ }

Notice that when you specify the type of a dictionary, then the order is a bit strange: value_type[key_type]. Well, when you want to access a value, we use this syntax: writeln(d[1]);, i.e. we indicate the key between the square brackets.

Passint a dictionary to a function

(2) passing to a function
def modify(d: dict) -> None: d[2] = "two" def main(): d = {} d[1] = "one" d[3] = "three" print(d) # {1: 'one', 3: 'three'} modify(d) print(d) # {1: 'one', 3: 'three', 2: 'two'}	import std.stdio; // notice the "ref" keyword void modify(ref string[int] d) { d[2] = "two"; } void main() { string[int] d; d[1] = "one"; d[3] = "three"; writeln(d); // [3:"three", 1:"one"] modify(d); writeln(d); // [3:"three", 2:"two", 1:"one"] }

In D, if you want to change a dictionary in a function, pass it by reference. Then the caller will see the changes.

Another solution would be to return the modified dictionary from the function. Then, on the caller side you should write d = modify(d);

Remove an element; remove all elements

(3) remove element(s)
def main(): d = {} d[1] = "one" d[2] = "two" d[3] = "three" print(d) # {1: 'one', 2: 'two', 3: 'three'} del d[2] print(d) # {1: 'one', 3: 'three'} # del d[2] # KeyError exception, no such key d.clear() print(d) # {}	import std.stdio; void main() { string[int] d; d[1] = "one"; d[2] = "two"; d[3] = "three"; writeln(d); // [3:"three", 2:"two", 1:"one"] d.remove(2); // returns true, key found writeln(d); // [3:"three", 1:"one"] d.remove(2); // returns false, no such key writeln(d); // [3:"three", 1:"one"] d.clear(); writeln(d); // [] }

In Python, when you want to remove an element by using a non-existing key, you get an error. In D, the function remove() returns false in this case.

The `in` operator

(4) in
def main(): d = {} d[1] = "one" d[2] = "two" d[3] = "three" print(d) # {1: 'one', 2: 'two', 3: 'three'} if 2 in d: print("2 was found") # will be printed if 9 not in d: print("9 was not found") # will be printed	import std.stdio; void main() { string[int] d; d[1] = "one"; d[2] = "two"; d[3] = "three"; writeln(d); // [3:"three", 2:"two", 1:"one"] if (2 in d) { writeln("2 was found"); // will be printed } if (9 !in d) { writeln("9 was not found"); // will be printed } }

The `get()` function

(5) `get()`
def main(): d = {} d[1] = "one" d[2] = "two" d[3] = "three" print(d) # {1: 'one', 2: 'two', 3: 'three'} # print(d[9]) # KeyError, no such key print(d.get(9)) # None print(d.get(9, "not found")) # "not found"	import std.stdio; void main() { string[int] d; d[1] = "one"; d[2] = "two"; d[3] = "three"; writeln(d); // [3:"three", 2:"two", 1:"one"] // writeln(d[9]); // error, no such key // writeln(d.get(9)); // error, no such function // a default value MUST be provided writeln(d.get(9, "not found")); // "not found" }

Length, keys, values

(6) length, keys, values

def main():
d = {}
d[1] = "one"
d[2] = "two"
d[3] = "three"
print(d) # {1: 'one', 2: 'two', 3: 'three'}

# 1
print(len(d)) # 3, number of key/value pairs

# 2
key_list = list(d.keys())
print(key_list) # [1, 2, 3]

# 3
value_list = list(d.values())
print(value_list) # ['one', 'two', 'three']

# 4
for k in d.keys(): # loop over an iterator
print(k)

# 5
for k in d: # same as before (loop over the keys)
print(k)

# 6
for v in d.values(): # loop over an iterator
print(v)

# 7
for k, v in d.items(): # loop over an iterator
print(k, "->", v)

import std.stdio;

void main()
{
string[int] d;
d[1] = "one";
d[2] = "two";
d[3] = "three";
writeln(d); // [3:"three", 2:"two", 1:"one"]

// 1
writeln(d.length); // 3, number of key/value pairs

// 2
writeln(d.keys()); // [3, 2, 1], as list

// 3
writeln(d.values()); // ["three", "two", "one"], as list

// 4; no list is created; we loop over a range
foreach (k; d.byKey) {
writeln(k);
}

// 5; !!! it iterates over the VALUES !!!
foreach (v; d) {
writeln(v);
}

// 6; no list is created; we loop over a range
foreach (v; d.byValue) {
writeln(v);
}

// 7a
foreach (k, v; d) {
writeln(k, " -> ", v);
}

// 7b; unpacking doesn't work here
foreach (pair; d.byKeyValue) {
writeln(pair.key, " -> ", pair.value);
}
}

The by*() functions return a range, not a list.

Create a dictionary; read/write

Passint a dictionary to a function

Remove an element; remove all elements

The in operator

The get() function

Length, keys, values

The `in` operator

The `get()` function