I'm looping through the items in my database using C# .NET and I'm attempting to display different data dependant on if a column value matches any of the values in an array. Because my array could potentially have hundreds of values, I'd rather not create hundreds of different IF statements, if possible. Is there a simpler way to achieve this?
Here's some example code, where "Items" is my db data and "Categories" is a column of said data:
var categoryList = new List<int> { 1, 2, 3, 4 };
foreach(var item in Items){
if(item.Categories.Any(x => #categoryList.Equals(x))){
<p>Yes</p>
}else{
<p>No</p>
}
}
The answer I give is based on the answer of this question. I modified the code to your situation.
foreach(var item in Items)
{
bool hasCategory = categoryList.Any(x => item.Categories.Any(c => c.Id == x));
}
or for larger collections (performance-wise):
bool hasCategory = item.Categories.Select(c => c.Id)
.Intersect(categoryList)
.Any();
Edit:
At first I thought item.Categories was a collection of IDs or something but then I started doubting. If item.Categories is just a single integer, following code will work:
foreach(var item in Items)
{
if(categoryList.Any(x => x == item.Categories))
<p>Yes</p>
else
<p>No</p>
}
Related
I need to iterate through all items in a subtree.
Therefore, I want to put all childItems of an predecessor into an array. I tried:
var successors =
TabWebContext.MenuItemSet.Where(m => m.PredecessorId == parentId).ToArray();
I also tried it without .ToArray() and with .ToList().
I have the following loop: while (successors.Count()>0){...} (or rather .Length>0).
The condition is never true.
What do you think am I making wrong? I know there are elements (if I do .FirstOrDefault(), there is at least one element found.
Why do you feel that it needs to be in an array to iterate through it? You could iterate the list like this:
foreach (var successor in TabWebContext.MenuItemSet.Where(m => m.PredecessorId == parentId))
{
// do stuff with 'successor'
}
Just to show an example of how select all from data source works with where clause.
int[] numbers = { 2, 34, 23, 11 }; //data source >> can be EF or ADO.NET
var result = numbers.Where(n => n <= 20).ToList(); // select all with filteration
foreach(int i in result ) //just to loop and
{
Console.WriteLine(i);
}
output :
22
11
so there is no issue can be seen in var successors =
TabWebContext.MenuItemSet.Where(m => m.PredecessorId == parentId).ToArray();
if you do facing an error then show that in your question.
I need to optimize the below foreach loop. The foreach loop is taken more time to get the unique items.
Instead can the FilterItems be converted into a list collection. If so how to do it. Then i will take unique items easily from it.
The problem arises when i have 5,00,000 items in FilterItems.
Please suggest some ways to optimize the below code:
int i = 0;
List<object> order = new List<object>();
List<object> unique = new List<object>();
// FilterItems IS A COLLECTION OF RECORDS. CAN THIS BE CONVERTED TO A LIST COLLECTION DIRECTLY, SO THAT I CAN TAKE THE UNIQUE ITEMS FROM IT.
foreach (Record rec in FilterItems)
{
string text = rec.GetValue(“Column Name”);
int position = order.BinarySearch(text);
if (position < 0)
{
order.Insert(-position - 1, text);
unique.Add(text);
}
i++;
}
It's unclear what you mean by "converting FilterItems into a list" when we don't know anything about it, but you could definitely consider sorting after you've got all the items, rather than as you go:
var strings = FilterItems.Select(record => record.GetValue("Column Name"))
.Distinct()
.OrderBy(x => x)
.ToList();
The use of Distinct() here will avoid sorting lots of equal items - it looks like you only want distinct items anyway.
If you want unique to be in the original order but order to be the same items, just sorted, you could use:
var unique = FilterItems.Select(record => record.GetValue("Column Name"))
.Distinct()
.ToList();
var order = unique.OrderBy(x => x).ToList();
Now Distinct() isn't guaranteed to preserve order - but it does so in the current implementation, and that's the most natural implementation, too.
I have list i.e. List<Field>. This Field class contains a code and a value properties among other fields and I would like to be able to use linq in order to sum up all the values for the same code.
I know I could loop through my list and add this to a dictionary using the following code, but I'm sure there has to be a cleaner way to do this:
if (totals.ContainsKey(code))
{
totals[code] += value;
}
else
{
totals.Add(code, value);
}
Any ideas?
I found something similar, but this applied to a list> which isn't what I have:
var result = Sales.SelectMany(d => d) // Flatten the list of dictionaries
.GroupBy(kvp => kvp.Key, kvp => kvp.Value) // Group the products
.ToDictionary(g => g.Key, g => g.Sum());
from this article [Sum amount using Linq in <List<Dictionary<string, int>>]Sum amount using Linq in <List<Dictionary<string, int>>
Any ideas? I could always change my code to have a Dictionary<string, Field> but I'm sure there has to be a way to do this with a list and linq.
Thanks.
I have list i.e. List<Field>. This Field class contains a code and a value properties among other fields and I would like to be able to use linq in order to sum up all the values for the same code.
I know I could loop through my list and add this to a dictionary using the following code, but I'm sure there has to be a cleaner way to do this:
if (totals.ContainsKey(code))
{
totals[code] += value;
}
else
{
totals.Add(code, value);
}
Any ideas?
I found something similar, but this applied to a list> which isn't what I have:
var result = Sales.SelectMany(d => d) // Flatten the list of dictionaries
.GroupBy(kvp => kvp.Key, kvp => kvp.Value) // Group the products
.ToDictionary(g => g.Key, g => g.Sum());
from this article [Sum amount using Linq in <List<Dictionary<string, int>>]Sum amount using Linq in <List<Dictionary<string, int>>
Any ideas? I could always change my code to have a Dictionary<string, Field> but I'm sure there has to be a way to do this with a list and linq.
Thanks.
UPDATE:
Sorry, I think I omitted an important section in regards to the above. The list is contained within another list i.e. List> myitemList; which will contain other irrelevant fields which may require further filtering. I'm not sure???
NOTE: Sorry formatting is messed up once again!
To give a bit of context to this:
Item1 (of type List)
Item Name Value
(Item 1) Type 1
(Item 2) Description Test
(Item 3) Code A
(Item 4) Net 100.00
Item2 (of type List)
Item Name Value
(Item 1) Type 2
(Item 2) Description Test1
(Item 3) Code B
(Item 4) Net 95.55
Item3 (of type List)
Item Name Value
(Item 1) Type 2
(Item 2) Description Test2
(Item 3) Code A
(Item 4) Net 35.95
As you can see each list of type List contains 4 Field entries where my Field is defined with Name (String) and Value (Object)
Each of these list is then added to a main list. So I need to loop through the main list and in turn I want to end up with a dictionary what will contain the "Code" and sum of "Net" for each list. So at the end, I should just end up with
A, 135.95
B, 95.55
I don't know if the above make sense. I hope it does!
UPDATE
The fact that I'm dealing with a list> actually didn't make a different as I actually wanted to sum up one list at the time, so provide answer is correct! Thank you!
The code that you posted is almost what you need - for using it on the list you need to simplify it slightly:
var result = myList // No flattening
.GroupBy(x => x.Code) // Group the items by the Code
.ToDictionary(g => g.Key, g => g.Sum(v => v.Value)); // Total up the values
var list = new List<Field>
{
new Field { Code = "A", Value = 10 },
new Field { Code = "A", Value = 20 },
new Field { Code = "B", Value = 30 },
};
var dic = list
.GroupBy(z => z.Code)
.ToDictionary(z => z.Key, z => z.Sum(f => f.Value));
You can do:
Dictionary<string, int> dictionary =
list.GroupBy(r => r.ID)
.ToDictionary(grp => grp.Key, grp => grp.Sum(r => r.Value));
Considering you have class like:
public class MyClass
{
public string ID { get; set; }
public int Value { get; set; }
}
I wanted to ask for suggestions how I can simplify the foreach block below. I tried to make it all in one linq statement, but I couldn't figure out how to manipulate "count" values inside the query.
More details about what I'm trying to achieve:
- I have a huge list with potential duplicates, where Id's are repeated, but property "Count" is different numbers
- I want to get rid of duplicates, but still not to loose those "Count" values
- so for the items with the same Id I summ up the "Count" properties
Still, the current code doesn't look pretty:
var grouped = bigList.GroupBy(c => c.Id).ToList();
foreach (var items in grouped)
{
var count = 0;
items.Each(c=> count += c.Count);
items.First().Count = count;
}
var filtered = grouped.Select(y => y.First());
I don't expect the whole solution, pieces of ideas will be also highly appreciated :)
Given that you're mutating the collection, I would personally just make a new "item" with the count:
var results = bigList.GroupBy(c => c.Id)
.Select(g => new Item(g.Key, g.Sum(i => i.Count)))
.ToList();
This performs a simple mapping from the original to a new collection of Item instances, with the proper Id and Count values.
var filtered = bigList.GroupBy(c=>c.Id)
.Select(g=> {
var f = g.First();
f.Count = g.Sum(c=>c.Count);
return f;
});
I have a query which returns data for a number of dataseries in one lump.
I would like to split this data up into the data series id, by the dataseries id. The query cannot be changed.
Its not safe to assume that the data is ordered by the series id, so what would be the best way to do this? LINQ?
I suggest grouping the result by the DataSeriesId.
var groupedResult = QueryDatabase().GroupBy(item => item.DataSeriesId);
Now you can access the grouped data as follows. The example will just print all groups with all items.
foreach(var group in groupedResult)
{
Console.WriteLine("Group: " + group.Key);
foreach(var item in group)
{
Console.WriteLine(" Item: " + item);
}
}
Or you can group the database query result into a list of lists.
IList<IList<DataItem>> = QueryDatabase()
.GroupBy(item => item.DataSeriesId)
.Select(group => group.ToList())
.ToList();
Or you can build a dictionary from DataSeriesId to a list of data items from the database query result.
IDictionary<Int32, IList<DataItem>> = QueryDatabase()
.GroupBy(item => item.DataSeriesId)
.ToDictionary(group => group.DataSeriesId, group => group.ToList());
Or use Enumerable.ToLookUp() if you don't want to alter the dictionary later.
UPDATE
Just noticed the "Best practice" in the question an the "DataReader" tag. Well LINQ is easy to write and easy to get right but it is probably not the fastest solution. So depending on your requirements using LINQ might be a good or bad choice. I would prefer LINQ if performance is not (yet) an issue. Else I would consider building a dictionary from DataSeriesId to a list of data items while reading the data.
IDictionary<Int32, IList<DataItem>> result =
new Dictionary<Int32, IList<DataItem>>();
while (dataSource.DataAvailiable)
{
DataItem item = dataSource.ReadItem();
IList<DataItem> items;
if (!result.TryGetValue(item.DataSeriesId))
{
items = new List<DataItem>();
result.Add(item.DataSeriesId, items);
}
items.Add(item);
}