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Query syntax is rewritten by the compiler to the same series of method calls as the method chaining syntax, so there's nothing you can do in QS that you can't do in MCS. There are a few things that look a bit neater in QS - let being a prime example - but there's always a way to write the same query in MCS.
There are quite a few extension methods that don't have an equivalent query keyword, so there are things you can do in MCS that you can't do in QS.
LINQPad[^] is probably the best tool to compare the two syntaxes.
"These people looked deep within my soul and assigned me a number based on the order in which I joined."
- Homer
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Splendid, thanks for the info.
Regards,
Rob Philpott.
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Rob Philpott wrote: Is there anything you can do in one syntax that you can't in the other?
Possibly Cast<T>
For example:
T record = mappedRecords[typeof(T)].Cast<T>().Where(r => r.Row == row).Single();
But I'm not sure, I haven't seen any examples using query syntax. I suppose the point though is, you should cast before you query.
Marc
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The Cast<T> part isn't a problem for query syntax - you just declare the type on the variable in the from clause:
from T mappedRecord in mappedRecord[typeof(T)]
...
But there's no query syntax keyword for Single , so you still have to call that as a method:
T record = (from T mappedRecord in mappedRecords[typeof(T)]
where mappedRecord.Row == row
select mappedRecord).Single();
I think the method chaining syntax is much cleaner - especially if you use the overload of Single to eliminate the Where call:
T record = mappedRecords[typeof(T)].Cast<T>().Single(r => r.Row == row);
"These people looked deep within my soul and assigned me a number based on the order in which I joined."
- Homer
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You're not missing anything. I trialled Linq functions extensively a couple of years back and they were always slower (sometimes markedly so) than the traditional methods they 'replace'. It all looks very fancy and sophisticated but it's totally inefficient.
I am not a number. I am a ... no, wait!
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You're missing out on a lot!
LINQ can be a bit slower, but it's awesome for many use cases.
When you really need the milliseconds go for regular ADO.NET, but how often do you really need that?
My experience with LINQ is not that it's slow to use, but that people suddenly forget that their LINQ expression becomes a SQL query and start writing the most horrible, non-indexed queries, now THAT is a performance killer.
What I really like about LINQ is that you can create your own extension methods and use those to create queries that read like regular sentences, or just a lot better than SQL in general (I mean, who remembers why all those WHERE clauses are there?)
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I think you're mistaking Linq with Linq to SQL.
Depending on the use case you might even gain performance, as an Enumerable is only evaluated when it's needed. As long as you're not accessing the items (or converting it into something other than an IEnumberable with "ToList" or "ToArray") the query isn't evaluated.
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Nicholas Marty wrote: I think you're mistaking Linq with Linq to SQL. I know the difference very well.
I was just assuming we were talking about LINQ to SQL/Entities/whatever data source, because if we're talking LINQ to Objects there really isn't any performance issue to talk about
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Depending on what you're doing with Linq, it can be even faster than a loop but it can also be slower by more than 100%.
If the difference matters is really up to the specific case. I'd guess it doesn't really have a noticeable impact in most cases, as a few milliseconds are negligible.
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Which "traditional" methods? ADO with DataSets?
From my experience, LINQ is trivially slower (but with added type-safety benefits to offset it).
BUT, linq makes it very easy to write bad queries. Things like, reading an entire table into an array, and then linearly search through it.
SO, it you compare a carefully tuned, DBA written stored procedure against a simple query written by a developer with little experience with databases, well, then, LINQ is going to lose. But, it you compare two well-crafted queries, one in LINQ and one in SQL, then you should be nearly the same (since the LINQ will generate the exact same SQL).
Truth,
James
modified 9-Jun-16 10:53am.
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OriginalGriff wrote: I can't get my head round the Linq syntax, so I always use method chaining.
I tend to use both, depending on what I'm doing. For example, this:
var categoryRanks = (from gs in geekSkills
where (gs.ProfileId == profile.Id)
join s in skills on gs.SkillId equals s.Id
select new { Level = gs.Level, CategoryId = s.CategoryId } into gss
join c in categories on gss.CategoryId equals c.Id
select new { Level = gss.Level, Name = c.Name } into gssc
group gssc by new { gssc.Name, gssc.Level } into g
select new SkillLevelBySkillByCategory() {
SkillLevel = g.Key.Level,
SkillLevelCount = g.Count(x => x.Level == g.Key.Level),
Name = g.Key.Name });
seems more readable to me than method chaining, but I also do things like this:
T record = mappedRecords[typeof(T)].Cast<T>().Where(r => r.Row == row).Single();
because here, it flows better.
Marc
Marc
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Same here, I never got the hang of it - never liked it to be honest, and always use C# method syntax.
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Ah, you might like the LINQ to objects book[^] then, it is brilliant. (At least I think it is )
Tons of useful tips in it, and a very nice read as well.
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Yeah, let is great.
Sometimes I convert a query from method syntax to query syntax just so I can use let
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Hi Marc,
I first became aware of the 'Let and 'Into Linq operators through this 2011 CP article (which I down-voted for "lack of original content"): [^]. I have never used them because I have never invested the energy to learn to use the "fuller" query syntax (my bad).
Your comment makes me wonder what I am missing (other than motivation).
cheers, Bill
p.s. the Microsoft example of 'Let you cite imho goes to a lot trouble do this:
string[] strings =
{
"A penny saved is a penny earned.",
"The early bird catches the worm.",
"The pen is mightier than the sword."
};
string vowels = "aeiou";
List<string> vowelstartwords = String.Join(" ", strings)
.Split(' ')
.Distinct()
.Where(word => vowels.Contains(Char.ToLower(word[0])))
.ToList(); That example, taken as a programming challenge, interests me: it leaves me wondering if it could be significantly improved in terms of memory use and execution time, and if the Linq code using 'Let would, in fact, improve those usage parameters.
«There is a spectrum, from "clearly desirable behaviour," to "possibly dodgy behavior that still makes some sense," to "clearly undesirable behavior." We try to make the latter into warnings or, better, errors. But stuff that is in the middle category you don’t want to restrict unless there is a clear way to work around it.» Eric Lippert, May 14, 2008
modified 8-Jun-16 14:41pm.
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I'd be inclined to avoid joining the strings just to split them again.
I'd also be inclined to use an array of char , rather than searching a string - although I doubt it would make much difference.
You've also added a Distinct and a ToList which weren't in the original example.
char[] vowels = { 'a', 'e', 'i', 'o', 'u' };
IEnumerable<string> vowelStartWords = strings
.SelectMany(sentence => sentence.Split(' '))
.Where(word => Array.IndexOf(vowels, char.ToLower(word[0])) != -1)
;
"These people looked deep within my soul and assigned me a number based on the order in which I joined."
- Homer
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I'm always delighted to have a chance to learn from your code !
I did add the call to 'Distinct with my first (and only) edit of the original post because I got to thinking that if you had a lot of 'if and 'else and 'and and 'is and 'or, etc., that would eliminate some duplicate calls.
edit ... my head spins as I consider the ways you can use Linq to "coalesce collections:" ''SelectMany, 'Aggregate, 'Join, etc.
thanks, Bill
«There is a spectrum, from "clearly desirable behaviour," to "possibly dodgy behavior that still makes some sense," to "clearly undesirable behavior." We try to make the latter into warnings or, better, errors. But stuff that is in the middle category you don’t want to restrict unless there is a clear way to work around it.» Eric Lippert, May 14, 2008
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Console.WriteLine(
string.Join(
"\n",
strings.SelectMany(sentence => sentence.Split(' '))
.Where(word => Array.IndexOf(vowels, char.ToLower(word[0])) != -1)
.Select(vowelWord => $"\"{vowelWord}\" starts with a vowel")))
;
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Shame there's no foreach extension method:
public static class EnumerableExtensions
{
public static void ForEach<T>(this IEnumerable<T> source, Action<T> action)
{
if (source == null) throw new ArgumentNullException(nameof(source));
if (action == null) throw new ArgumentNullException(nameof(action));
foreach (T item in source)
{
action(item);
}
}
}
Then you could do:
strings.SelectMany(sentence => sentence.Split(' '))
.Where(word => Array.IndexOf(vowels, char.ToLower(word[0])) != -1)
.Select(vowelWord => $"\"{vowelWord}\" starts with a vowel")
.ForEach(Console.WriteLine)
;
"These people looked deep within my soul and assigned me a number based on the order in which I joined."
- Homer
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Well, you could convert the IEnumerable to a List with ToList and call the ForEach method of the List<T> class. Should pretty much equal the foreach loop (as you need to evaluate the query anyways when looping)
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I actually thought about a nasty Linq-with-side-effect version with something like
.Select(vowelWord => Console.WriteLine($"\"{vowelWord}\" starts with a vowel"))
but of course you can't, because Console.WriteLine() returns Void. No doubt it would be possible to force something like this, but that'd be silly; it's actually quite neat that C# protects us from such folly. For one thing, it won't evaluate until the IEnumerable is enumerated, so you don't really know when that is just from that line of code.
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Marc, you probably know this by now, but let is just syntactic sugar for the Select method.
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Haha, I have to say I dunno "how to replace let with extension method" so when I want to introduce a variable it's one case where I definitely use linq query syntax over chaining LINQ extension methods....
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For a bit of background. LINQ facilitates functors and monads (concepts from functional programming). Simplified: functors are types that 'map' (Select), monads are types that 'bind' (SelectMany).
When you do 'from x in y' you're lifting the value out of the monad (get the value wrapped up *in* the monad), doing an operation on it, and then wrapping it back up in the monad. The monad in this case being IEnumerable/IQueryable.
There are other types, like Option<t>, Either<l,r>, Try<t> - see this library: [language-ext]
'let' is essentially the non-monadic assign, it's essentially exactly the same as declaring a local variable. It doesn't do the lifting, and therefore if you did 'let x = list', then it wouldn't extract the value from the list, it will just assign the list.
It's most useful in query expressions to pre-calculate a value that will be used many times in subsequent parts of the query; but it can very much allow full functional programming within LINQ expressions.
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