LINQ
目次
where句
int[] array = { 3, -5, -1, 0, 2 };
foreach (int elm in array) Console.WriteLine(elm);
→3, -5, -1, 0, 2
クエリ変数 = クエリ式
var pos =
from n in array
where n > 0
select n;
foreach (int elm in pos) Console.WriteLine(elm);
→3, 2
int[] array = { 3, -5, -1, 0, 2 };
var pos = array.Where(n => n > 0).Select(n => n);
foreach (int elm in pos) Console.WriteLine(elm);
→3, 2
orderby句
var pos =
from n in array
where n > 0
orderby n
foreach (int elm in pos) Console.WriteLine(elm);
→2, 3
orderby n ascending ※デフォルト
orderby n descending
var pos = array.Where(n => n > 0).OrderBy(n => n).Select(n => n);
foreach (int elm in pos) Console.WriteLine(elm);
→2, 3
～OrderBy(n => n)
～OrderByDescending(n => n)
select句
要素を加工して指定
var pos =
from n in array
select Math.Abs(n) ※abs:絶対値
select n;
foreach (int elm in pos) Console.WriteLine(elm);
→3, 5, 1, 0, 2
要素を加工して指定
var pos = array.Select(n => Math.Abs(n)).OrderBy(n => n);
foreach (int elm in pos) Console.WriteLine(elm);
→0, 1, 2, 3, 5
クラス要素を指定
{
public int myInt { get; private set; }
public MyClass(int prm)
{
this.myInt = prm;
}
}
static void Main(string[] args)
{
MyClass[] myClass = {
new MyClass(5),
new MyClass(10),
new MyClass(15)
};
var myInt =
from n in myClass
select n.myInt;
foreach (var elm in myInt) Console.WriteLine(elm);
→5, 10, 15
}
{
public int myInt { get; private set; }
public MyClass(int prm)
{
this.myInt = prm;
}
}
static void Main(string[] args)
{
MyClass[] myClass = {
new MyClass(5),
new MyClass(10),
new MyClass(15)
};
var pos = myClass.Select(n => n.myInt);
foreach (var elm in myInt) Console.WriteLine(elm);
→5, 10, 15
}
別クラスのインスタンスを指定
{
public int herInt { get; private set; }
public HerClass(int prm)
{
this.herInt = prm*2;
}
}
static void Main(string[] args)
{
MyClass[] myClass = {
new MyClass(5),
new MyClass(10),
new MyClass(15)
};
var myInt =
from n in myClass
select new HerClass(n.myInt);
foreach (var elm in myInt) Console.WriteLine(elm.herInt);
→10, 20, 30
}
{
public int herInt { get; private set; }
public HerClass(int prm)
{
this.herInt = prm*2;
}
}
static void Main(string[] args)
{
MyClass[] myClass = {
new MyClass(5),
new MyClass(10),
new MyClass(15)
};
var pos = myClass.Select(n => new HerClass(n.myInt));
foreach (var elm in myInt) Console.WriteLine(elm.herInt);
→10, 20, 30
}
group句
var place =
from n in array
group n by n.Substring(2);
3文字目で分類
foreach (var elm in place)
{
// 親要素.Key
Console.WriteLine(elm.Key);
// 子要素
foreach (var e in elm)
{
Console.WriteLine(e);
}
}
→
県 親要素.Key
兵庫県
奈良県
滋賀県
市 親要素.Key
西宮市
尼崎市
芦屋市
神戸市
大津市
彦根市
var pos = array.GroupBy(n => n.Substring(2));
3文字目で分類
foreach (var parent in pos)
foreach (var child in parent )
Console.WriteLine(child);
→
兵庫県
奈良県
滋賀県
西宮市
尼崎市
芦屋市
神戸市
大津市
彦根市
join句
select句にfrom句の要素を指定
{
public int ItemId { get; private set; }
public string ItemNm { get; private set; }
public Item(int prmId, string prmNm)
{
this.ItemId = prmId;
this.ItemNm = prmNm;
}
}
class StockInfo
{
public int ItemId { get; private set; }
public bool InStock { get; private set; }
public StockInfo(int prmId, bool prmInStock)
{
this.ItemId = prmId;
this.InStock = prmInStock;
}
}
static void Main(string[] args)
{
Item[] items = {
new Item(prmId: 1, prmNm: @”C#”),
new Item(prmId: 2, prmNm: @”JavaScript”),
new Item(prmId: 3, prmNm: @”C++”)
};
StockInfo[] stockInfo = {
new StockInfo(prmId: 1, prmInStock: true),
new StockInfo(prmId: 2, prmInStock: false),
new StockInfo(prmId: 3, prmInStock: true)
};
var list =
from item in items
join info in stockInfo
on item.ItemId equals info.ItemId
where info.InStock == true
select item.ItemNm;
foreach (var elm in list) Console.WriteLine(elm);
}
→
C#
C++
select句に別クラスのインスタンスを指定
{
public string ItemNm { get; private set; }
public bool InStock { get; private set; }
public ItemList(string prmNm, bool prmInStock)
{
this.ItemNm = prmNm;
this.InStock = prmInStock;
}
}
static void Main(string[] args)
{
var list =
from item in items
join info in stockInfo
on item.ItemId equals info.ItemId
select new ItemList(prmNm:item.ItemNm, prmInStock: info.InStock);
foreach (var elm in list)
{
Console.WriteLine(elm.ItemNm + “:” + elm.InStock);
}
}
→
C#:True
JavaScript:False
C++:True
{
public string ItemNm { get; private set; }
public bool InStock { get; private set; }
public ItemList(string prmNm, bool prmInStock)
{
this.ItemNm = prmNm;
this.InStock = prmInStock;
}
}
static void Main(string[] args)
{
var list = items.Join(
stockInfo,
n => n.ItemId,
m => m.ItemId,
(n, m) => new ItemList(prmNm: n.ItemNm, prmInStock:m.InStock));
foreach (var elm in list) Console.WriteLine(elm.ItemNm + ":" + elm.InStock);
}
→
C#:True
JavaScript:False
C++:True
select句に匿名クラスのインスタンスを指定
{
var list =
from item in items
join info in stockInfo
on item.ItemId equals info.ItemId
select new { ItemNm = item.ItemNm, InStock = info.InStock };
foreach (var elm in list)
{
Console.WriteLine(elm.ItemNm + “:” + elm.InStock);
}
}
→
C#:True
JavaScript:False
C++:True
{
var list = items.Join(
stockInfo,
n => n.ItemId,
m => m.ItemId,
(n, m) => new { ItemNm = n.ItemNm, InStock = m.InStock });
foreach (var elm in list) Console.WriteLine(elm.ItemNm + ":" + elm.InStock);
}
→
C#:True
JavaScript:False
C++:True
クエリの実行タイミング
int[] array = { 3, -5, -1, 0, 2 };
var pos =
from n in array
where n > 0
select n;
この時点ではクエリは実行されておらず、クエリ変数に値は格納されていない
foreach (int elm in pos) Console.WriteLine(elm);
→3, 2
array[1] *= -1;
array[2] *= -1;
データソースを変更
foreach (int elm in pos) Console.WriteLine(elm);
→3, 5, 1, 2
データソース：クエリ式が変化するとクエリ変数も変化している。
into：クエリの接続
from n in array
group n by n.Substring(2)
into m
where m.Count() <= 3
要素数が3以下のグループに絞る
select m;
foreach (var elm in place)
{
foreach (var e in elm) Console.WriteLine(e);
}
→
兵庫県
奈良県
滋賀県
let：クエリ変数
var strs =
from n in strArray
select n;
foreach (var elm in strs) Console.WriteLine(elm);
→
西宮
尼崎
芦屋
var chrs =
from n in strArray
let chrArray = n.ToCharArray()
文字列型要素→char型配列 へ変換し、クエリ変数に格納
from m in chrArray
select m;
foreach (var elm in chrs) Console.WriteLine(elm);
→
西
宮
尼
崎
芦
屋
例(2)
string[] strArray = { "兵庫県", "西宮市", "尼崎市", "奈良県", "芦屋市", "神戸市", "滋賀県", "大津市", "彦根市" };
var strs =
from n in strArray
let place = n.Substring(2)
where place.Equals("県")
select n
into m
select m;
foreach (var elm in strs) Console.WriteLine(elm);
→
兵庫県
奈良県
滋賀県
Follow me!
