Suppose I have the following list:
var strings = new List<string>();
strings.Add("1");
strings.Add("12.456");
strings.Add("Foobar");
strings.Add("0.56");
strings.Add("zero");
Is there some sort of query I can write in Linq that will return to me only the numeric items, i.e. the 1st, 2nd, and 4th items from the list?
-R.
strings.Where(s => { double ignored; return double.TryParse(s, out ignored); })
This will return all the strings that are parseable as doubles as strings. If you want them as numbers (which makes more sense), you could write an extension method:
public static IEnumerable<double> GetDoubles(this IEnumerable<string> strings)
{
foreach (var s in strings)
{
double result;
if (double.TryParse(s, out result))
yield return result;
}
}
Don't forget that double.TryParse() uses your current culture, so it will give different results on different computers. If you don't want that, use double.TryParse(s, NumberStyles.AllowDecimalPoint, CultureInfo.InvariantCulture, out result).
Try this:
double dummy = 0;
var strings = new List<string>();
strings.Add("1");
strings.Add("12.456");
strings.Add("Foobar");
strings.Add("0.56");
strings.Add("zero");
var numbers = strings.Where(a=>double.TryParse(a, out dummy));
You could use a simple predicate to examine each string, like so:
var strings = new List<string>();
strings.Add("1");
strings.Add("12.456");
strings.Add("Foobar");
strings.Add("0.56");
strings.Add("zero");
var nums = strings.Where( s => s.ToCharArray().All( n => Char.IsNumber( n ) || n == '.' ) );
Related
How can i split text which contains only brackets, commas and 3 integers. For example:
{5,40,30}
I also want to validate that it looks like above.
Try this using regex.
var testString = "12,23,{23,23},23,{51,22,345}{{]}1123,{12,12,232,123}{{33,33,33}}";
var regex = new Regex(#"{\d+,\d+,\d+}");
var matches = regex.Matches(testString);
The output of the above test string after match is
{51,22,345} and {33,33,33}
Here's a non regex solution using string methods and LINQ which i prefer:
string text = "{5,40,30}";
bool valid = text.StartsWith("{") && text.EndsWith("}");
int[] integers = {};
if (valid)
{
integers = text.Trim('{', '}').Split(',')
.Select(s => s.TryGetInt32())
.Where(nullInt => nullInt.HasValue)
.Select(nullInt => nullInt.Value)
.ToArray();
valid = integers.Length == 3;
}
using this handy extension method that i use in LINQ queries to get a Nullabel<int> from a string, so similar to int.TryParse but with an int?.
public static int? TryGetInt32(this string item)
{
int i;
bool success = int.TryParse(item, out i);
return success ? (int?)i : (int?)null;
}
In C# .NET 4.0, I am struggling to come up with the most efficient way to determine if the contents of 2 lists of items contain any differences.
I don't need to know what the differences are, just true/false whether the lists are different based on my criteria.
The 2 lists I am trying to compare contain FileInfo objects, and I want to compare only the FileInfo.Name and FileInfo.LastWriteTimeUtc properties of each item. All the FileInfo items are for files located in the same directory, so the FileInfo.Name values will be unique.
To summarize, I am looking for a single Boolean result for the following criteria:
Does ListA contain any items with FileInfo.Name not in ListB?
Does ListB contain any items with FileInfo.Name not in ListA?
For items with the same FileInfo.Name in both lists, are the FileInfo.LastWriteTimeUtc values different?
Thank you,
Kyle
I would use a custom IEqualityComparer<FileInfo> for this task:
public class FileNameAndLastWriteTimeUtcComparer : IEqualityComparer<FileInfo>
{
public bool Equals(FileInfo x, FileInfo y)
{
if(Object.ReferenceEquals(x, y)) return true;
if (x == null || y == null) return false;
return x.FullName.Equals(y.FullName) && x.LastWriteTimeUtc.Equals(y.LastWriteTimeUtc);
}
public int GetHashCode(FileInfo fi)
{
unchecked // Overflow is fine, just wrap
{
int hash = 17;
hash = hash * 23 + fi.FullName.GetHashCode();
hash = hash * 23 + fi.LastWriteTimeUtc.GetHashCode();
return hash;
}
}
}
Now you can use a HashSet<FileInfo> with this comparer and HashSet<T>.SetEquals:
var comparer = new FileNameAndLastWriteTimeUtcComparer();
var uniqueFiles1 = new HashSet<FileInfo>(list1, comparer);
bool anyDifferences = !uniqueFiles1.SetEquals(list2);
Note that i've used FileInfo.FullName instead of Name since names aren't unqiue at all.
Sidenote: another advantage is that you can use this comparer for many LINQ methods like GroupBy, Except, Intersect or Distinct.
This is not the most efficient way (probably ranks a 4 out of 5 in the quick-and-dirty category):
var comparableListA = ListA.Select(a =>
new { Name = a.Name, LastWrite = a.LastWriteTimeUtc, Object = a});
var comparableListB = ListB.Select(b =>
new { Name = b.Name, LastWrite = b.LastWriteTimeUtc, Object = b});
var diffList = comparableListA.Except(comparableListB);
var youHaveDiff = diffList.Any();
Explanation:
Anonymous classes are compared by property values, which is what you're looking to do, which led to my thinking of doing a LINQ projection along those lines.
P.S.
You should double check the syntax, I just rattled this off without the compiler.
string[] sArray = { APPLE|apple, SOURCE|source, BIOS|bios, APPLE|device };
Above is the string array, and I need to split these array and get before values of pipe symbol **|** using LINQ.
Now am using like this to get into array:
List<string> lVirtualDir = new List<string>();
foreach (string _sArray in sArray)
{
lVirtualDir.Add(_sArray.Remove(cus.IndexOf('|'), _sArray.Length - _sArray.IndexOf('|')));
}
This above code will get result as
APPLE
SOURCE
BIOS
APPLE
I need to sort this code part in LINQ.
This should do it:
lVirtualDir = sArray.Select(x => x.Split('|')[0].Trim())
.OrderBy(x => x).ToList();
I have a file that I want to read into an array.
string[] allLines = File.ReadAllLines(#"path to file");
I know that I can iterate through the array and find each line that contains a pattern and display the line number and the line itself.
My question is:
Is it possible to do the same thing with LINQ?
Well yes - using the Select() overload that takes an index we can do this by projecting to an anonymous type that contains the line itself as well as its line number:
var targetLines = File.ReadAllLines(#"foo.txt")
.Select((x, i) => new { Line = x, LineNumber = i })
.Where( x => x.Line.Contains("pattern"))
.ToList();
foreach (var line in targetLines)
{
Console.WriteLine("{0} : {1}", line.LineNumber, line.Line);
}
Since the console output is a side effect it should be separate from the LINQ query itself.
Using LINQ is possible. However, since you want the line number as well, the code will likely be more readable by iterating yourself:
const string pattern = "foo";
for (int lineNumber = 1; lineNumber <= allLines.Length; lineNumber++)
{
if (allLines[lineNumber-1].Contains(pattern))
{
Console.WriteLine("{0}. {1}", lineNumber, allLines[i]);
}
}
something like this should work
var result = from line in File.ReadAllLines(#"path")
where line.Substring(0,1) == "a" // put your criteria here
select line
Let's say I have an array, and I want to do a LINQ query against a varchar that returns any records that have an element of the array anywhere in the varchar.
Something like this would be sweet.
string[] industries = { "airline", "railroad" }
var query = from c in contacts where c.industry.LikeAnyElement(industries) select c
Any ideas?
This is actually an example I use in my "Express Yourself" presentation, for something that is hard to do in regular LINQ; As far as I know, the easiest way to do this is by writing the predicate manually. I use the example below (note it would work equally for StartsWith etc):
using (var ctx = new NorthwindDataContext())
{
ctx.Log = Console.Out;
var data = ctx.Customers.WhereTrueForAny(
s => cust => cust.CompanyName.Contains(s),
"a", "de", "s").ToArray();
}
// ...
public static class QueryableExt
{
public static IQueryable<TSource> WhereTrueForAny<TSource, TValue>(
this IQueryable<TSource> source,
Func<TValue, Expression<Func<TSource, bool>>> selector,
params TValue[] values)
{
return source.Where(BuildTrueForAny(selector, values));
}
public static Expression<Func<TSource, bool>> BuildTrueForAny<TSource, TValue>(
Func<TValue, Expression<Func<TSource, bool>>> selector,
params TValue[] values)
{
if (selector == null) throw new ArgumentNullException("selector");
if (values == null) throw new ArgumentNullException("values");
if (values.Length == 0) return x => true;
if (values.Length == 1) return selector(values[0]);
var param = Expression.Parameter(typeof(TSource), "x");
Expression body = Expression.Invoke(selector(values[0]), param);
for (int i = 1; i < values.Length; i++)
{
body = Expression.OrElse(body,
Expression.Invoke(selector(values[i]), param));
}
return Expression.Lambda<Func<TSource, bool>>(body, param);
}
}
from c in contracts
where industries.Any(i => i == c.industry)
select c;
something like that. use the any method on the collection.
IEnumerable.Contains() translates to SQL IN as in:
WHERE 'american airlines' IN ('airline', 'railroad') -- FALSE
String.Contains() which translates to SQL LIKE %...% as in:
WHERE 'american airlines' LIKE '%airline%' -- TRUE
If you want the contacts where the contact's industry is LIKE (contains) any of the given industries, you want to combine both Any() and String.Contains() into something like this:
string[] industries = { "airline", "railroad" };
var query = from c in contacts
where industries.Any(i => c.Industry.Contains(i))
select c;
However, combining both Any() and String.Contains() like this is NOT supported in LINQ to SQL. If the set of given industries is small, you can try something like:
where c.Industry.Contains("airline") ||
c.Industry.Contains("railroad") || ...
Or (although normally not recommended) if the set of contacts is small enough, you could bring them all from the DB and apply the filter with LINQ to Objects by using contacts.AsEnumerable() or contacts.ToList() as the source of the query above:
var query = from c in contacts.AsEnumerable()
where industries.Any(i => c.Industry.Contains(i))
select c;
it will work if you build up the query as follows:
var query = from c in contacts.AsEnumerable()
select c;
query = query.Where(c=> (c.Industry.Contains("airline")) || (c.Industry.Contains("railroad")));
you just need to programmatically generate the string above if the parameters airline and railroad are user inputs. This was in fact a little more complicated than I was expecting. See article - http://www.albahari.com/nutshell/predicatebuilder.aspx
Unfortunately, LIKE is not supported in LINQ to SQL as per here:
http://msdn.microsoft.com/en-us/library/bb882677.aspx
To get around this, you will have to write a stored procedure which will accept the parameters you want to use in the like statement(s) and then call that from LINQ to SQL.
It should be noted that a few of the answers suggest using Contains. This won't work because it looks to see that the entire string matches the array element. What is being looked for is for the array element to be contained in the field itself, something like:
industry LIKE '%<element>%'
As Clark has mentioned in a comment, you could use a call to IndexOf on each element (which should translate to a SQL call):
string[] industries = { "airline", "railroad" }
var query =
from c in contacts
where
c.industry.IndexOf(industries[0]) != -1 ||
c.industry.IndexOf(industries[1]) != -1
If you know the length of the array and the number of elements, then you could hard-code this. If you don't, then you will have to create the Expression instance based on the array and the field you are looking at.