I'm new to Java so if this has already been answered somewhere else then I either don't know enough to search for the correct things or I just couldn't understand the answers.
So the question being:
I have a bunch of objects in a list:
try(Stream<String> logs = Files.lines(Paths.get(args))) {
return logs.map(LogLine::parseLine).collect(Collectors.toList());
}
And this is how the properties are added:
LogLine line = new LogLine();
line.setUri(matcher.group("uri"));
line.setrequestDuration(matcher.group("requestDuration"));
....
How do I sort logs so that I end up with list where objects with same "uri" are displayed only once with average requestDuration.
Example:
object1.uri = 'uri1', object1.requestDuration = 20;
object2.uri = 'uri2', object2.requestDuration = 30;
object3.uri = 'uri1', object3.requestDuration = 50;
Result:
object1.uri = 'uri1', 35;
object2.uri = 'uri2', 30;
Thanks in advance!
Take a look at Collectors.groupingBy and Collectors.averagingDouble. In your case, you could use them as follows:
Map<String, Double> result = logLines.stream()
.collect(Collectors.groupingBy(
LogLine::getUri,
TreeMap::new,
Collectors.averagingDouble(LogLine::getRequestDuration)));
The Collectors.groupingBy method does what you want. It is overloaded, so that you can specify the function that returns the key to group elements by, the factory that creates the returned map (I'm using TreeMap here, because you want the entries ordered by key, in this case the URI), and a downstream collector, which collects the elements that match the key returned by the first parameter.
If you want an Integer instead of a Double value for the averages, consider using Collectors.averagingInt.
This assumes LogLine has getUri() and getRequestDuration() methods.
Related
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 want to extract part of a collection to another collection.
I can easily do the same using a for loop, but my linq query is not working for the same.
I am a neophyte in Linq, so please help me correcting the query (if possible with explanation / beginners tutorial link)
Legacy way of doing :
Collection<string> testColl1 = new Collection<string> {"t1", "t2", "t3", "t4"};
Collection<string> testColl2 = new Collection<string>();
for (int i = 0; i < newLength; i++)
{
testColl2.Add(testColl1[i]);
}
Where testColl1 is the source & testColl2 is the desired truncated collection of count = newLength.
I have used the following linq queries, but none of them are working ...
var result = from t in testColl1 where t.Count() <= newLength select t;
var res = testColl1.Where(t => t.Count() <= newLength);
Use Enumerable.Take:
var testColl2 = testColl1.Take(newLength).ToList();
Note that there's a semantic difference between your for loop and the version using Take. The for loop will throw with IndexOutOfRangeException exception if there are less than newLength items in testColl1, whereas the Take version will silently ignore this fact and just return as many items up to newLength items.
The correct way is by using Take:
var result = testColl1.Take(newLength);
An equivalent way using Where is:
var result = testColl1.Where((i, item) => i < newLength);
These expressions will produce an IEnumerable, so you might also want to attach a .ToList() or .ToArray() at the end.
Both ways return one less item than your original implementation does because it is more natural (e.g. if newLength == 0 no items should be returned).
You could convert to for loop to something like this:
testColl1.Take(newLength)
Use Take:
var result = testColl1.Take(newLength);
This extension method returns the first N elements from the collection where N is the parameter you pass, in this case newLength.
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).
I am attempting to get unique values in a list of similar value distinguished only by a one element in a pipe delimited string... I keep getting at least one object must implement Icomparable. I don't understand why I keep getting that. I am able to groupBy that value... Why can't I find the max... I guess it is looking for something to compare it with. If I get the integer version will it stop yelling at me? This is the last time I am going to try using LINQ...
var queryResults = PatientList.GroupBy(x => x.Value.Split('|')[1]).Select(x => x.Max());
I know I can get the unique values some other way. I am just having a hard time figuring it out. In that List I know that the string with the highest value amongst its similar brethren is the one that I want to add to the list. How can I do that? I am totally drawing a blank because I have been trying to get this to work in linq for the last few days with no luck...
foreach (XmlNode node in nodeList)
{
XmlDocument xDoc = new XmlDocument();
xDoc.LoadXml(node.OuterXml);
string popPatInfo = xDoc.SelectSingleNode("./template/elements/element[#name=\"FirstName\"]").Attributes["value"].Value + ", " + xDoc.SelectSingleNode("./template/elements/element[#name=\"LastName\"]").Attributes["value"].Value + " | " + DateTime.Parse(xDoc.SelectSingleNode("./template/elements/element[#name=\"DateOfBirth\"]").Attributes["value"].Value.Split('T')[0]).ToString("dd-MMM-yyyy");
string patientInfo = xDoc.SelectSingleNode("./template/elements/element[#name=\"PatientId\"]").Attributes["value"].Value + "|" + xDoc.SelectSingleNode("./template/elements/element[#name=\"PopulationPatientID\"]").Attributes["enc"].Value;// +"|" + xDoc.SelectSingleNode("./template/elements/element[#name=\"AdminDate\"]").Attributes["value"].Value;
int enc = Int32.Parse(patientInfo.Split('|')[1]);
if (enc > temp)
{
lastEncounter.Add(enc, patientInfo);
temp = enc;
}
//lastEncounter.Add(Int32.Parse(patientInfo.Split('|')[1]));
PatientList.Add( new SelectListItem { Text = popPatInfo, Value = patientInfo });
}
I was thinking about using some kind of temp variable to find out what is the highest value and then add that string to the List. I am totally drawing a blank however...
Here I get the IDs in an anonymous type to make it readable.
var patientEncounters= from patient in PatientList
let PatientID=Int32.Parse(patient.Value.Split('|')[0])
let EncounterID=Int32.Parse(patient.Value.Split('|')[1])
select new { PatientID, EncounterID };
Then we group by UserID and get the last encounter
var lastEncounterForEachUser=from pe in patientEncounters
group pe by pe.PatientID into grouped
select new
{
PatientID=grouped.Key,
LastEncounterID=grouped.Max(g=>g.EncounterID)
};
Linq doesn't know how to compare 2 Patient objects, so it can't determine which one is the "greatest". You need to make the Patient class implement IComparable<Patient>, to define how Patient objects are compared.
// Compare objets by Id value
public int CompareTo(Patient other)
{
return this.Id.CompareTo(other.Id);
}
Another option is to use the MaxBy extension method available in Jon Skeet's MoreLinq project:
var queryResults = PatientList.GroupBy(x => x.Value.Split('|')[1])
.Select(x => x.MaxBy(p => p.Id));
EDIT: I assumed there was a Patient class, but reading your code again, I realize it's not the case. PatientList is actually a collection of SelectListItem, so you need to implement IComparable in that class.
I have the following object:
Line{ String Content; Type type;}
And I have, IQeryable<Line> lines, which I perform operations against. I selected certain lines where line.Content.Contains('x') = list1, and now am trying to get to the rest of the lines i.e. lines - list1 and for this am using
list2 = lines.Except(list1);
but that results in list2 = lines.
Code:
private
IQueryable<Line>
ExtractLines(
IQueryable<Line> allLines,
String keyword,
ref IQueryable<Line> hits)
{
hits = allLines.Where(lx => lx.Content.Contains(keyword));
return allLines.Except(hits);
}
any ideas?
Alright. All I needed to do is to implement IEqualityComparer<T> in Line class.
lines is IQeryable<Line>. If you do not save its result, it will run every time you select from it. If Line does not override Equals and ==, that will create different objects each time, so Except cannot remove the previous object from new objects.
Now, a lot is missing, but try:
var linesList = lines.ToList(); // get results ones
var hasX = lines.Where(line => line.Content.Contains('x'));
var noX = lines.Except(hasX);