请教List求交集的Linq问题
2
悬赏园豆：20
[已解决问题]
解决于 2012-02-22 10:06
代码如下：
class Program
{
static void Main(string[] args)
{
List<A> aList = new List<A>()
{
new A(){ Id=1,Names=new List<string>(){"a","b","c"}},
new A(){ Id=2,Names=new List<string>(){"b","c","d"}},
new A(){ Id=3,Names=new List<string>(){"c","d","e"}},
new A(){ Id=4,Names=new List<string>(){"d","e","f"}},
new A(){ Id=5,Names=new List<string>(){"e","f","g"}}
};
List<string> test = new List<string>() { "b", "f" };
var val=//求aList中Names属性与test有交集的A集合
Console.Read();
}
}
public class A
{
public int Id { get; set; }
public List<string> Names { get; set; }
}
请教代码中注释的部分的写法，也就是得出id为1、2、4、5的A的集合，谢谢，用linq写
最佳答案
4
var val = aList.FindAll(a => a.Names.Any(test.Contains));
收获园豆：15
吹毛求疵一下， FindAll不是LINQ的方法 - -
@水牛刀刀: 多谢提醒。那把FindAll换成where不就可以了。
var val = aList.Where(a => a.Names.Any(test.Contains));
@LCM: :)
@水牛刀刀: 不过我测了一下这三种的性能，你看下代码。
Stopwatch stw = new Stopwatch();
stw.Start();
for (int i = 0; i < 1000; i++)
{
var val = aList.FindAll(a => a.Names.Any(test.Contains));
}
stw.Stop();
Console.WriteLine(stw.ElapsedTicks);
//---------------------------------
stw.Reset();
stw.Start();
for (int i = 0; i < 1000; i++)
{
var val1 = aList.Where(a => a.Names.Any(test.Contains));
}
stw.Stop();
Console.WriteLine(stw.ElapsedTicks);
//---------------------------------
stw.Reset();
stw.Start();
for (int i = 0; i < 1000; i++)
{
var val2 = aList.Where(a => a.Names.Intersect(test, StringComparer.OrdinalIgnoreCase).Any()).ToList();
}
stw.Stop();
Console.WriteLine(stw.ElapsedTicks);
结果如下：
5539254
537250
15661632
@LCM: 第二种，你ToList一下，应该跟第一种差不多的。第三种多遍历了数据，所以会最慢。
@水牛刀刀: 嗯
@LCM:
如果不区分大小写，前两种方法可以实现吗？
@乱世文章:
var val1 = aList.Where(a => a.Names.Any(n => test.Any(t => t.Equals(n, StringComparison.InvariantCultureIgnoreCase)));
@水牛刀刀: 正解
其他回答(2)
1
var val = aList.Where(a => a.Names.Intersect(test, StringComparer.OrdinalIgnoreCase).Any()).ToList();
收获园豆：5
这种写法会遍历test，而不是像楼上的那种，找到就会停止了。
1
public class newArray<K> implements List<K>{ private Object[] a = new Object[8]; private int at = 0; private void setSize(Object[] a,int index){ if( index > a.length-1 ){ int times = (int) Math.ceil((float)index/(float)(a.length-1)); int length = (int)times *(a.length); Object[] b = new Object[length]; for(int i = 0 ; i < a.length ; i++){ b[i] = (K)a[i]; } this.a = b; } } public String toString(){ StringBuffer Str = new StringBuffer().append("["); boolean isFirst = true; for(int i = 0 ; i < at ; i++ ){ if(isFirst){ isFirst = false; }else{ Str.append(" , "); } Str.append((K)a[i]); } Str.append("]"); return Str.toString(); } @Override public boolean add(K e) { setSize(a,at); a[at] = e ; at++; return false; } @Override public void add(int index, K element) { if( at > index ){ a[index] = element; }else{ throw new IndexOutOfBoundsException("Index:"+index+", Size: "+at); } } @Override public boolean addAll(Collection<? extends K> c) { Object[] o = c.toArray();// TODO Auto-generated method stub for(int i = 0 ; i < o.length ; i++ ){ add((K)o[i]); } return false; } @Override public boolean addAll(int index, Collection<? extends K> c) { if( (at-1) < index ){ throw new IndexOutOfBoundsException("Index:"+index+", Size: "+at); } Object[] o = c.toArray();// TODO Auto-generated method stub this.at = index; for(int i = 0 ; i < o.length ; i++ ){ add((K)o[i]); } return false; } @Override public void clear() { this.a = new Object[8]; this.at = 0; } @Override public boolean contains(Object o) { if(o != null){ for(int i = 0 ; i < at ; i++ ){ if( ((K)o).equals((K)a[i]) || (K)o == (K)a[i] ) return true ; } }else{ for(int i = 0 ; i < at ; i++ ){ if(a[i] == null) return true ; } } return false; } @Override public boolean containsAll(Collection<?> c) { Object[] o = c.toArray();// TODO Auto-generated method stub for(int i = 0 ; i < o.length ; i++ ){ if(!contains(o[i])) return false; } return true; } @Override public K get(int index) { if( at > index ){ return (K)a[index]; }else{ throw new IndexOutOfBoundsException("Index:"+index+", Size: "+at); } } @Override public int indexOf(Object o) { int j = -1; if(o != null){ for(int i = 0 ; i < at ; i++ ){ if(((K)o).equals((K)a[i])) return i ; } }else{ for(int i = 0 ; i < at ; i++ ){ if(a[i] == null) return i ; } } return -1; } @Override public int lastIndexOf(Object o) { int j = -1; if(o != null){ for(int i = (at-1) ; i > -1 ; i-- ){ if(((K)o).equals((K)a[i])) return i ; } }else{ for(int i = (at-1) ; i > -1 ; i-- ){ if(a[i] == null) return i ; } } return -1; } @Override public boolean isEmpty() { return (at==0); } @Override public Iterator<K> iterator() { Iterator<K> i = new Iterator<K>() { private int now = 0; @Override public boolean hasNext() { return ( now < at ); } @Override public K next() { K k = (K)a[now]; now++; return k; } @Override public void remove() { } }; return i; } @Override public ListIterator<K> listIterator() { ListIterator<K> i = new ListIterator<K>() { private int now = 0; @Override public void add(K e) { } @Override public boolean hasNext() { return ( now < at ); } @Override public boolean hasPrevious() { return (now > 0); } @Override public K next() { K k = (K)a[now]; now++; return k; } @Override public int nextIndex() { if(now < ( at - 1 ) ){ return now+1; }else{ return -1; } } @Override public K previous() { if(now > 0 ){ return (K)a[now-1]; }else{ throw new IndexOutOfBoundsException("iterator is at the begainest"); } } @Override public int previousIndex() { if(now > 0 ){ return now-1; }else{ return -1; } } @Override public void remove() { // TODO Auto-generated method stub } @Override public void set(K e) { // TODO Auto-generated method stub } }; return null; } @Override public ListIterator<K> listIterator(int index) { // TODO Auto-generated method stub return null; } @Override public boolean remove(Object o) { int i = indexOf(o); while(i != -1){ remove(i); i = indexOf(o); }; return false; } @Override public K remove(int index) { for(int j = index ; j < at ; j++ ){ a[j] = a[j+1]; } at--; return null; } @Override public boolean removeAll(Collection<?> c) { Iterator<K> i = (Iterator<K>) c.iterator(); while(i.hasNext()){ remove((K)i.next()); } return false; } @Override public boolean retainAll(Collection<?> c) { return false; } @Override public K set(int index, K element) { add( index, element); return null; } @Override public int size() { return at; } @Override public List<K> subList(int fromIndex, int toIndex) { List<K> result = new newArray<K>(); if( toIndex < fromIndex ){ throw new IndexOutOfBoundsException("fromIndex:"+fromIndex+", toIndex: "+toIndex); } if( (at-1) < fromIndex ){ throw new IndexOutOfBoundsException("fromIndex:"+fromIndex+", Size: "+at); } if(toIndex > at) toIndex = at; for(int i = fromIndex ; i < toIndex ; i++){ result.add((K)a[i]); } return result; } @Override public Object[] toArray() { Object[] arr = new Object[at]; for(int i = 0 ; i < at ; i++){ arr[i] = a[i]; } return arr; } @Override public <T> T[] toArray(T[] a) { a = (T[]) toArray(); return null; } }
