C# Groupby Linq 和 foreach
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C# Groupby Linq and foreach
提问by IEnumerable
I need a more efficient way of producing multiple files from my data group.
Im using a List<MyObject>type and my object has some public properties in which I need to group the data by.
我需要一种更有效的方法来从我的数据组中生成多个文件。我使用一种List<MyObject>类型，我的对象有一些公共属性，我需要在其中对数据进行分组。
I have heard of Linqand it sounds like something I could use. However Im not sure how to go about it.
我听说过Linq，它听起来像我可以使用的东西。但是我不知道如何去做。
I need to produce a text file for each STATE, so grouping all the MyObjects(people) by state, then running a foreachlook on them to build the TEXT file.
我需要为每个州生成一个文本文件，因此将所有MyObjects（人）按州分组，然后foreach查看他们以构建文本文件。
void Main()
{
List<MyObject> lst = new List<MyObject>();
lst.Add(new MyObject{ name = "bill", state = "nsw", url = "microsoft.com"});
lst.Add(new MyObject{ name = "ted", state = "vic", url = "apple.com"});
lst.Add(new MyObject{ name = "jesse", state = "nsw", url = "google.com"});
lst.Add(new MyObject{ name = "james", state = "qld", url = "toshiba.com"});
string builder = "";
foreach (MyObject item in myObjects) {
builder += item.name + "\r\n";
builder += item.url + "\r\n" + "\r\n\r\n";
}
and out to the `StreamWriter` will be the filenames by state.
In total for the above data I need 3 files;
对于上述数据，我总共需要 3 个文件；
-nsw.txt
-vic.txt
-qld.txt
采纳答案by lesscode
Something like this, perhaps?
像这样的东西，也许？
var groups = lst.GroupBy(x => x.state);
foreach (var group in groups)
{
using (var f = new StreamWriter(group.Key + ".txt"))
{
foreach (var item in group)
{
f.WriteLine(item.name);
f.WriteLine(item.url);
}
}
}
回答by iamkrillin
You def. could use LINQ here.
你确定。可以在这里使用 LINQ。
lst.GroupBy(r=> r.state).ToList().ForEach(r=> {
//state= r.Key
//
foreach (var v in r)
{
}
});
The thing about linq. If you want to know how to do something in it. Think "how would I do this in SQL". The keywords are for the most part the same.
关于 linq 的事情。如果您想知道如何在其中做某事。想想“我将如何在 SQL 中做到这一点”。关键字大部分是相同的。
回答by user568021
Something like...
就像是...
string builderNsw = "";
foreach (MyObject item in lst.Where(o=>o.state == 'nsw')) {
builderNsw += item.name + "\r\n";
builderNsw += item.url + "\r\n" + "\r\n\r\n";
}
...but there are probably many ways to achieve this.
...但可能有很多方法可以实现这一目标。
回答by k.m
You can actually produce entire content with LINQ:
您实际上可以使用 LINQ 生成整个内容：
var entryFormat = "{1}{0}{2}{0}{0}{0}";
var groupsToPrint = lst
.GroupBy(p => p.state)
.Select(g => new
{
State = g.Key,
// produce file content on-the-fly from group entries
Content = string.Join("", g.Select(v => string.Format(entryFormat,
Environment.NewLine, v.name, v.url)))
});
var fileNameFormat = "{0}.txt";
foreach (var entry in groupsToPrint)
{
var fileName = string.Format(fileNameFormat, entry.State);
File.WriteAllText(fileName, entry.Content);
}
回答by Arun Prasad E S
Same as Above - Iterating through groups by group, can get group name also
同上 - 按组遍历组，也可以获得组名
int itemCounter = 1;
IEnumerable<DataRow> sequence = Datatables.AsEnumerable();
var GroupedData = from d in sequence group d by d["panelName"]; // GroupedData is now of type IEnumerable<IGrouping<int, Document>>
foreach (var GroupList in GroupedData) // GroupList = "document group", of type IGrouping<int, Document>
{
bool chk = false;
foreach (var Item in GroupList)
{
if (chk == false) // means when header is not inserted
{
var groupName = "Panel Name : " + Item["panelName"].ToString();
chk = true;
}
var count = itemCounter.ToString();
var itemRef = Item["reference"].ToString();
itemCounter++;
}
}
