I want to sort a list of strings (with possibly duplicate entries) by using as ordering reference the order of the entries in another list. So, the following list is the list I want to sort
List<String> list = ['apple','pear','apple','x','x','orange','x','pear'];
And the list that specifies the order is
List<String> order = ['orange','apple','x','pear'];
And the output should be
List<String> result = ['orange','apple','apple','x','x','x','pear','pear'];
Is there a clean way of doing this?
I don't understand if I can use list's sort and compare with the following problem. I tried using map, iterable, intersection, etc.
There might be a more efficient way but at least you get the desired result:
main() {
List<String> list = ['apple','pear','apple','x','x','orange','x','pear'];
List<String> order = ['orange','apple','x','pear'];
list.sort((a, b) => order.indexOf(a).compareTo(order.indexOf(b)));
print(list);
}
Try it on DartPad
The closure passed to list.sort(...) is a custom comparer which instead of comparing the passed item, compares their position in order and returns the result.
Using a map for better lookup performance:
main() {
List<String> list = ['apple','pear','apple','x','x','orange','x','pear'];
List<String> orderList = ['orange','apple','x','pear'];
Map<String,int> order = new Map.fromIterable(
orderList, key: (key) => key, value: (key) => orderList.indexOf(key));
list.sort((a, b) => order[a].compareTo(order[b]));
print(list);
}
Try it on DartPad
Related
I am trying to sort that simple list of users by "created". What am I doing wrong?
val user1 = User("2019-01-01 17:42:34")
val user2 = User("2019-01-02 17:42:34")
val user3 = User("2019-01-03 17:42:34")
val list = listOf(user2, user3, user1)
list.sortedWith(compareBy {
LocalDateTime.parse(
it.created,
DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss")
)
})
data class User(val created: String = "")
Your code works. The problem here is that sortedWith returns a new list with the results of the sorting! Check the documentation:
Returns a list of all elements sorted according to the specified [comparator].
The sort is stable. It means that equal elements preserve their order relative to each other after sorting.
So if you want to sort the collection itself you need to use a MutableList and sortWith:
val list = mutableListOf(User("2019-01-01 17:42:34"), User("2019-01-02 17:42:34"), User("2019-01-03 17:42:34"))
list.sortWith(compareBy {
LocalDateTime.parse(
it.created,
DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"))
})
sortedWith function returns a new list with sorted elements without modifying the original collection. You probably want to use sortWith function of MutableList that sorts the original collection.
I have an Action method in my controller which returns a List Object
Public ActionResult GetCats(long Id,string strsortorder,string dltIds)
{
var Result=objrepo.GetCats(Id);//this method returns me List of Result
}
My array looks like this:
var Result=[{CatId:1015,CatName:Abc},{CatId:1016,CatName:Acd},
{CatId:1017,CatName:Adf},{CatId:1018,CatName:CDdf},{CatId:1019,CatName:asdas},
{CatId:1020,CatName:Abc},{CatId:1021,CatName:Abc},{CatId:1022,CatName:Abc},
{CatId:1023,CatName:Abc},{CatId:1024,CatName:Abc}]
What I want to do is:
Using two more parameters in my Action Method "strsortorder" and "dltIds"
that have a list of ids like this:
strsortorder="1021,1015,1016,1019,1022";
dltIds="1017,1018,1020";
From this the "Result" returned from my method , I want to remove the records which are in "dltids" and the remaining array should be sorted in the order which I have in "strsortorder";
In the end the new object should look like this:
var NewResult=[{CatId:1021,CatName:Abc},{CatId:1015,CatName:Abc},
{CatId:1016,CatName:Acd},{CatId:1019,CatName:asdas},{CatId:1022,CatName:Abc},
{CatId:1023,CatName:Abc},{CatId:1024,CatName:Abc}]
Can any one help me in acheiving this in linq or any other way?
I want to avoid any type of loop or froeach here for max extent, I know it can be done by looping but I want to avoid this since the result can sometimes contain large amounts of data.
I realized you can use an ArrayList instead of a Dictionary and it would be faster. I think Dictionary is clear how it works but here is the "better" implementation using array list:
var excludeList = dltIds.Split(",".ToCharArray());
ArrayList sortList = new ArrayList(strsortorder.Split(",".ToCharArray()));
var NewResult =
Result.Where(item => ! excludeList.Contains(item.CatId.ToString()))
.OrderBy(item => {
if (sortList.Contains(item.CatId.ToString()))
return sortList.IndexOf(item.CatId.ToString());
return sortList.Count;
});
Original answer below:
Public ActionResult GetCats(long Id,string strsortorder,string dltIds)
{
var Result=objrepo.GetCats(Id);//this method returns me List of Result
var excludeList = dltIds.Split(",".ToCharArray());
int orderCount = 0; // used in the closure creating the Dictionary below
var sortList = strsortorder.Split(",".ToCharArray())
.ToDictionary(x => x,x => orderCount++);
// filter
var NewResult =
Result.Where(item => ! excludeList.Contains(item.CatId.ToString()))
.OrderBy(item => {
if (sortList.ContainsKey(item.CatId.ToString()))
return sortList[item.CatId.ToString()];
return sortList.Count();
});
}
How this works:
First I create lists out of your comma separated exclude list using split.
This I create a dictionary with the key being the ordering ID and the value being an integer that goes up by one.
For the filtering I look to see if an item is in the exclude array before I continue processing the item.
I then do a sort on matching against the key and the dictionary and returning the value -- this will sort things in the order of the list since I incremented a counter when creating the values. If an item is not in the dictionary I return one more than the maximum value in the dictionary which must be the count of the items. (I could have used the current value of orderCount instead.)
Questions?
I have a program with multiple int variables where individual counts are added to the specific variable each time a set fail condition is encountered. I want the user to be able to track how many failures of each category they have encountered by a button click. I want to display the range on a datagridview in order from highest value integer down to lowest. I also need to display in the adjacent column the name of the test step that relates to the value. My plan was to use Array.sort to order the integers but i then lose track of their names so cant assign the adjacent string column. I tried using a hashtable but if i use the string as a key it sorts alphabetically not numerically and if i use the integer as a key i get duplicate entries which dont get added to the hash table. here is some of the examples i tried but they have the aforementioned problems. essentially i want to end with two arrays where the order matches the naming and value convention. FYI the variables were declared before this section of code, variables ending in x are the string name for the (non x) value of the integer.
Hashtable sorter = new Hashtable();
sorter[download] = downloadx;
sorter[power] = powerx;
sorter[phase] = phasex;
sorter[eeprom] = eepromx;
sorter[upulse] = upulsex;
sorter[vpulse] = vpulsex;
sorter[wpulse] = wpulsex;
sorter[volts] = voltsx;
sorter[current] = currentx;
sorter[ad] = adx;
sorter[comms] = commsx;
sorter[ntc] = ntcx;
sorter[prt] = prtx;
string list = "";
string[] names = new string[13];
foreach (DictionaryEntry child in sorter)
{
list += child.Value.ToString() + "z";
}
int[] ordered = new int[] { download, power, phase, eeprom, upulse, vpulse, wpulse, volts, current, ad, comms, ntc, prt };
Array.Sort(ordered);
Array.Reverse(ordered);
for (int i = 0; i < sorter.Count; i++)
{
int pos = list.IndexOf("z");
names[i] = list.Substring(0, pos);
list = list.Substring(pos + 1);
}
First question here so hope its not too longwinded.
Thanks
Use a Dictionary. And you can order it by the value : myDico.OrderBy(x => x.Value).Reverse(), the sort will be numerical descending. You just have to enumerate the result.
I hope I understand your need. Otherwise ignore me.
You want to be using a
Dictionary <string, int>
to store your numbers.I'm not clear on how you're displaying results at the end - do you have a grid or a list control?
You ask about usings. Which ones do you already have?
EDIT for .NET 2.0
There might be a more elegant solution, but you could implement the logic by putting your rows in a DataTable. Then you can make a DataView of that table and sort by whichever column you like, ascending or descending.
See http://msdn.microsoft.com/en-us/library/system.data.dataview(v=VS.80).aspx for example.
EDIT for .NET 3.5 and higher
As far as sorting a Dictionary by its values:
var sortedEntries = myDictionary.OrderBy(pair => pair.Value);
If you need the results to be a Dictionary, you can call .ToDictionary() on that. For reverse order, use .OrderByDescending(pair => pair.Value).
Can anyone explain what the difference is between:
tmp = invoices.InvoiceCollection
.OrderBy(sort1 => sort1.InvoiceOwner.LastName)
.OrderBy(sort2 => sort2.InvoiceOwner.FirstName)
.OrderBy(sort3 => sort3.InvoiceID);
and
tmp = invoices.InvoiceCollection
.OrderBy(sort1 => sort1.InvoiceOwner.LastName)
.ThenBy(sort2 => sort2.InvoiceOwner.FirstName)
.ThenBy(sort3 => sort3.InvoiceID);
Which is the correct approach if I wish to order by 3 items of data?
You should definitely use ThenBy rather than multiple OrderBy calls.
I would suggest this:
tmp = invoices.InvoiceCollection
.OrderBy(o => o.InvoiceOwner.LastName)
.ThenBy(o => o.InvoiceOwner.FirstName)
.ThenBy(o => o.InvoiceID);
Note how you can use the same name each time. This is also equivalent to:
tmp = from o in invoices.InvoiceCollection
orderby o.InvoiceOwner.LastName,
o.InvoiceOwner.FirstName,
o.InvoiceID
select o;
If you call OrderBy multiple times, it will effectively reorder the sequence completely three times... so the final call will effectively be the dominant one. You can (in LINQ to Objects) write
foo.OrderBy(x).OrderBy(y).OrderBy(z)
which would be equivalent to
foo.OrderBy(z).ThenBy(y).ThenBy(x)
as the sort order is stable, but you absolutely shouldn't:
It's hard to read
It doesn't perform well (because it reorders the whole sequence)
It may well not work in other providers (e.g. LINQ to SQL)
It's basically not how OrderBy was designed to be used.
The point of OrderBy is to provide the "most important" ordering projection; then use ThenBy (repeatedly) to specify secondary, tertiary etc ordering projections.
Effectively, think of it this way: OrderBy(...).ThenBy(...).ThenBy(...) allows you to build a single composite comparison for any two objects, and then sort the sequence once using that composite comparison. That's almost certainly what you want.
I found this distinction annoying in trying to build queries in a generic manner, so I made a little helper to produce OrderBy/ThenBy in the proper order, for as many sorts as you like.
public class EFSortHelper
{
public static EFSortHelper<TModel> Create<TModel>(IQueryable<T> query)
{
return new EFSortHelper<TModel>(query);
}
}
public class EFSortHelper<TModel> : EFSortHelper
{
protected IQueryable<TModel> unsorted;
protected IOrderedQueryable<TModel> sorted;
public EFSortHelper(IQueryable<TModel> unsorted)
{
this.unsorted = unsorted;
}
public void SortBy<TCol>(Expression<Func<TModel, TCol>> sort, bool isDesc = false)
{
if (sorted == null)
{
sorted = isDesc ? unsorted.OrderByDescending(sort) : unsorted.OrderBy(sort);
unsorted = null;
}
else
{
sorted = isDesc ? sorted.ThenByDescending(sort) : sorted.ThenBy(sort)
}
}
public IOrderedQueryable<TModel> Sorted
{
get
{
return sorted;
}
}
}
There are a lot of ways you might use this depending on your use case, but if you were for example passed a list of sort columns and directions as strings and bools, you could loop over them and use them in a switch like:
var query = db.People.AsNoTracking();
var sortHelper = EFSortHelper.Create(query);
foreach(var sort in sorts)
{
switch(sort.ColumnName)
{
case "Id":
sortHelper.SortBy(p => p.Id, sort.IsDesc);
break;
case "Name":
sortHelper.SortBy(p => p.Name, sort.IsDesc);
break;
// etc
}
}
var sortedQuery = sortHelper.Sorted;
The result in sortedQuery is sorted in the desired order, instead of resorting over and over as the other answer here cautions.
if you want to sort more than one field then go for ThenBy:
like this
list.OrderBy(personLast => person.LastName)
.ThenBy(personFirst => person.FirstName)
Yes, you should never use multiple OrderBy if you are playing with multiple keys.
ThenBy is safer bet since it will perform after OrderBy.
I'm trying to use LINQ to return a list of ids given a list of objects where the id is a property. I'd like to be able to do this without looping through each object and pulling out the unique ids that I find.
I have a list of objects of type MyClass and one of the properties of this class is an ID.
public class MyClass
{
public int ID { get; set; }
}
I want to write a LINQ query to return me a list of those Ids.
How do I do that, given an IList<MyClass> such that it returns an IEnumerable<int> of the ids?
I'm sure it must be possible to do it in one or two lines using LINQ rather than looping through each item in the MyClass list and adding the unique values into a list.
IEnumerable<int> ids = list.Select(x=>x.ID).Distinct();
Use the Distinct operator:
var idList = yourList.Select(x=> x.ID).Distinct();
Using straight LINQ, with the Distinct() extension:
var idList = (from x in yourList select x.ID).Distinct();
When taking Distinct, we have to cast into IEnumerable too. If the list is <T> model, it means you need to write code like this:
IEnumerable<T> ids = list.Select(x => x).Distinct();
int[] numbers = {1,2,3,4,5,3,6,4,7,8,9,1,0 };
var nonRepeats = (from n in numbers select n).Distinct();
foreach (var d in nonRepeats)
{
Response.Write(d);
}
Output
1234567890