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Find longest string in Datatable column

Find longest string from DataReader columnWhat is the difference between String and string in C#?Hidden Features of C#?LINQ query on a DataTableCase insensitive 'Contains(string)'How do I get a consistent byte representation of strings in C# without manually specifying an encoding?Group By Multiple ColumnsFind intersecting DataRows in a List of DataTablesGet the sum of a datatable columnC# LINQ is taking DataTable AsEnumerable and changing the column datatypeSearch for an integer item in a datatable with string column values

.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty margin-bottom:0;

11

3

I would like to know If It's possible to create a "one-line" Linq to retrieve longest string value of specific Datatable column, meaning that all column data (numbers, dates,strings...) should be converted to string and then return longest string.

What I've found is only how to obtain longest string from a List, or max length value.

This is what I tried so far (error in Length):

string maxString = dt
 .AsEnumerable()
 .Select(row => row[mycolumn].ToString())
 .Where(s => s.OrderByDescending(st => st.Length).First());

c# linq

share|improve this question

edited Apr 15 at 7:38

Dmitry Bychenko

122k1515 gold badges115115 silver badges150150 bronze badges

asked Apr 15 at 7:17

Lucy82Lucy82

1801212 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  "This is what I tried so far (obviously not working)" > Not so obvious, please explain.
  
  – Patrick Hofman
  Apr 15 at 7:18
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @PatrickHofman, sorry, this code returns me "char does not contain a deifintion for Length"
  
  – Lucy82
  Apr 15 at 7:20
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  No need to use Where(). This should do the trick: .Select(row => row[mycolumn].ToString()).OrderByDescending(st => st.Length).First();
  
  – Stephan Bauer
  Apr 15 at 7:20
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @StephanBauer, that was fast. Thanks, I knew It had to be something simple as that :)
  
  – Lucy82
  Apr 15 at 7:24
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  If you are loading that datatable from a database you should probably consider writing SQL to do this instead. Loading an entire table into memory and processing it with Linq is probably a lot slower.
  
  – Marie
  Apr 15 at 13:26
  

  
  
  
  

add a comment
 | 

11

3

I would like to know If It's possible to create a "one-line" Linq to retrieve longest string value of specific Datatable column, meaning that all column data (numbers, dates,strings...) should be converted to string and then return longest string.

What I've found is only how to obtain longest string from a List, or max length value.

This is what I tried so far (error in Length):

string maxString = dt
 .AsEnumerable()
 .Select(row => row[mycolumn].ToString())
 .Where(s => s.OrderByDescending(st => st.Length).First());

c# linq

share|improve this question

edited Apr 15 at 7:38

Dmitry Bychenko

122k1515 gold badges115115 silver badges150150 bronze badges

asked Apr 15 at 7:17

Lucy82Lucy82

1801212 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  "This is what I tried so far (obviously not working)" > Not so obvious, please explain.
  
  – Patrick Hofman
  Apr 15 at 7:18
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @PatrickHofman, sorry, this code returns me "char does not contain a deifintion for Length"
  
  – Lucy82
  Apr 15 at 7:20
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  No need to use Where(). This should do the trick: .Select(row => row[mycolumn].ToString()).OrderByDescending(st => st.Length).First();
  
  – Stephan Bauer
  Apr 15 at 7:20
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @StephanBauer, that was fast. Thanks, I knew It had to be something simple as that :)
  
  – Lucy82
  Apr 15 at 7:24
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  If you are loading that datatable from a database you should probably consider writing SQL to do this instead. Loading an entire table into memory and processing it with Linq is probably a lot slower.
  
  – Marie
  Apr 15 at 13:26
  

  
  
  
  

add a comment
 | 

I would like to know If It's possible to create a "one-line" Linq to retrieve longest string value of specific Datatable column, meaning that all column data (numbers, dates,strings...) should be converted to string and then return longest string.

What I've found is only how to obtain longest string from a List, or max length value.

This is what I tried so far (error in Length):

string maxString = dt
 .AsEnumerable()
 .Select(row => row[mycolumn].ToString())
 .Where(s => s.OrderByDescending(st => st.Length).First());

c# linq

share|improve this question

edited Apr 15 at 7:38

Dmitry Bychenko

122k1515 gold badges115115 silver badges150150 bronze badges

asked Apr 15 at 7:17

Lucy82Lucy82

1801212 bronze badges

string maxString = dt
 .AsEnumerable()
 .Select(row => row[mycolumn].ToString())
 .Where(s => s.OrderByDescending(st => st.Length).First());

share|improve this question

edited Apr 15 at 7:38

Dmitry Bychenko

122k1515 gold badges115115 silver badges150150 bronze badges

asked Apr 15 at 7:17

Lucy82Lucy82

1801212 bronze badges

share|improve this question

edited Apr 15 at 7:38

Dmitry Bychenko

122k1515 gold badges115115 silver badges150150 bronze badges

asked Apr 15 at 7:17

Lucy82Lucy82

1801212 bronze badges

edited Apr 15 at 7:38

Dmitry Bychenko

122k1515 gold badges115115 silver badges150150 bronze badges

edited Apr 15 at 7:38

Dmitry Bychenko

122k1515 gold badges115115 silver badges150150 bronze badges

asked Apr 15 at 7:17

Lucy82Lucy82

1801212 bronze badges

asked Apr 15 at 7:17

Lucy82Lucy82

1801212 bronze badges

3 Answers
3

active

oldest

votes

10

You are almost there:

string maxString = dt.AsEnumerable()
 .Select(row => row[mycolumn].ToString())
 .OrderByDescending(st => st.Length).FirstOrDefault();

A Where expects a predicate (function that will return true or false). Instead just order the projection (the .Select) as you did and retrieve the first item.

---

Notice that is is an O(nlogn) solution which can be improved to an O(n) solution by not sorting but by finding the item with the max length. One possible way of doing so is an in Dimitry's answer. For less than huge collections I'm not sure one would really feel the difference but it is indeed worth noticing this.

---

See that you can also use MoreLinq's .MaxBy that can be added through Nuget (For the GitHub repo) which will both give you the O(n) performance and the desired "one-liner":

var row = dt.AsEnumerable().MaxBy(r => r[mycolumn].ToString().Length);

share|improve this answer

edited Apr 15 at 14:48

answered Apr 15 at 7:20

Gilad GreenGilad Green

31.3k55 gold badges3535 silver badges6060 bronze badges

• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  
  Isn't sorting to get the max a innefficient? Or does LINQ optimise that?
  
  – RoadRunner
  Apr 15 at 8:06
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @RoadRunner - you are right that sorting will be less efficient. This is an O(nlogn) solution while one can do O(n) as in the answer below. I tried to keep as close to the original as possible
  
  – Gilad Green
  Apr 15 at 8:55
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  IMO you should not recommend FirstOrDefault, you should recommend a sanity check first. Then you dont have to worry about null popping up.
  
  – Marie
  Apr 15 at 13:28
  

  
  
  
  

add a comment
 | 

15

You are looking for ArgMax - a value such that it has max value of some kind of property. Standard Linq doesn't provide ArgMax but you can implement it via Aggregate (i.e. get a single value from a sequence):

 string maxString = dt
 .AsEnumerable()
 .Select(row => row[mycolumn].ToString())
 .Aggregate((s, a) => a.Length > s.Length ? a : s);

share|improve this answer

edited Apr 15 at 12:36

answered Apr 15 at 7:36

Dmitry BychenkoDmitry Bychenko

122k1515 gold badges115115 silver badges150150 bronze badges

• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  This solution is likely much faster than the accepted answer since it doesn't have to actually sort the list, just iterate it once.
  
  – Marie
  Apr 15 at 13:29
  
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  @Marie yes, I tested, this is the fastest one. Though It differs for 1 second comparing to Gilad Green answer in my test for exporting data into Excel with OpenXML for 320k+ rows and 7 columns.
  
  – Lucy82
  Apr 16 at 7:27
  
  

  
  
  
  

add a comment
 | 

3

First of all do not use AsEnumerable right after dt..
Write somehow like this:

dt.OrderByDescending(row => row[mycolumn].Length).First();

share|improve this answer

answered Apr 15 at 8:09

NoImaginationNoImagination

17811 silver badge77 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  AsEnumerable shouldn't be used because it transfers calculations to app memory, when my example forces it to perform calculations at sql server. When all calculations done First() transfers the result to app memory. Try my example and tell me if it works, ok?
  
  – NoImagination
  Apr 15 at 8:38
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @Lucy82, well i checked my example and it works perfectly :). But as people above noticed it would be much better to find Max value by aggregation function. It requires just 1 cycle when OrderBy sorts.
  
  – NoImagination
  Apr 15 at 12:39
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @Lucy82 Neither the accepted, nor Dmitry's, answer would be good for large datasets that are persisted in a database. Ie. if dt is a table in a database and contains thousands of rows the other answers would first fetch all those rows and then do the sorting to get the max value.
  
  – Taemyr
  Apr 15 at 12:44
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @NoImagination I might be wrong but the question isnt tagged entity or anything. Isn't "when my example forces it to perform calculations at sql server" only true if they are using an ORM that supports that functionality?
  
  – Marie
  Apr 15 at 13:31
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @NoImagination It stands to reason that "dt" stands for DataTable (the row[column] part also makes no sense at all for a EF query) which means that leaving the AsEnumerable off simply won't work. It also means that the data is already in memory so really nothing lost there.
  
  – Voo
  Apr 15 at 17:57
  
  

  
  
  
  

 | 
show 5 more comments

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10

You are almost there:

string maxString = dt.AsEnumerable()
 .Select(row => row[mycolumn].ToString())
 .OrderByDescending(st => st.Length).FirstOrDefault();

A Where expects a predicate (function that will return true or false). Instead just order the projection (the .Select) as you did and retrieve the first item.

---

Notice that is is an O(nlogn) solution which can be improved to an O(n) solution by not sorting but by finding the item with the max length. One possible way of doing so is an in Dimitry's answer. For less than huge collections I'm not sure one would really feel the difference but it is indeed worth noticing this.

---

See that you can also use MoreLinq's .MaxBy that can be added through Nuget (For the GitHub repo) which will both give you the O(n) performance and the desired "one-liner":

var row = dt.AsEnumerable().MaxBy(r => r[mycolumn].ToString().Length);

share|improve this answer

edited Apr 15 at 14:48

answered Apr 15 at 7:20

Gilad GreenGilad Green

31.3k55 gold badges3535 silver badges6060 bronze badges

• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  
  Isn't sorting to get the max a innefficient? Or does LINQ optimise that?
  
  – RoadRunner
  Apr 15 at 8:06
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @RoadRunner - you are right that sorting will be less efficient. This is an O(nlogn) solution while one can do O(n) as in the answer below. I tried to keep as close to the original as possible
  
  – Gilad Green
  Apr 15 at 8:55
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  IMO you should not recommend FirstOrDefault, you should recommend a sanity check first. Then you dont have to worry about null popping up.
  
  – Marie
  Apr 15 at 13:28
  

  
  
  
  

add a comment
 | 

10

You are almost there:

string maxString = dt.AsEnumerable()
 .Select(row => row[mycolumn].ToString())
 .OrderByDescending(st => st.Length).FirstOrDefault();

A Where expects a predicate (function that will return true or false). Instead just order the projection (the .Select) as you did and retrieve the first item.

---

Notice that is is an O(nlogn) solution which can be improved to an O(n) solution by not sorting but by finding the item with the max length. One possible way of doing so is an in Dimitry's answer. For less than huge collections I'm not sure one would really feel the difference but it is indeed worth noticing this.

---

See that you can also use MoreLinq's .MaxBy that can be added through Nuget (For the GitHub repo) which will both give you the O(n) performance and the desired "one-liner":

var row = dt.AsEnumerable().MaxBy(r => r[mycolumn].ToString().Length);

share|improve this answer

edited Apr 15 at 14:48

answered Apr 15 at 7:20

Gilad GreenGilad Green

31.3k55 gold badges3535 silver badges6060 bronze badges

• 
  
  
  

  
  3
  

  
  
  
  
  
  

  
  
  Isn't sorting to get the max a innefficient? Or does LINQ optimise that?
  
  – RoadRunner
  Apr 15 at 8:06
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @RoadRunner - you are right that sorting will be less efficient. This is an O(nlogn) solution while one can do O(n) as in the answer below. I tried to keep as close to the original as possible
  
  – Gilad Green
  Apr 15 at 8:55
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  IMO you should not recommend FirstOrDefault, you should recommend a sanity check first. Then you dont have to worry about null popping up.
  
  – Marie
  Apr 15 at 13:28
  

  
  
  
  

add a comment
 | 

You are almost there:

string maxString = dt.AsEnumerable()
 .Select(row => row[mycolumn].ToString())
 .OrderByDescending(st => st.Length).FirstOrDefault();

A Where expects a predicate (function that will return true or false). Instead just order the projection (the .Select) as you did and retrieve the first item.

---

Notice that is is an O(nlogn) solution which can be improved to an O(n) solution by not sorting but by finding the item with the max length. One possible way of doing so is an in Dimitry's answer. For less than huge collections I'm not sure one would really feel the difference but it is indeed worth noticing this.

---

See that you can also use MoreLinq's .MaxBy that can be added through Nuget (For the GitHub repo) which will both give you the O(n) performance and the desired "one-liner":

var row = dt.AsEnumerable().MaxBy(r => r[mycolumn].ToString().Length);

share|improve this answer

edited Apr 15 at 14:48

answered Apr 15 at 7:20

Gilad GreenGilad Green

31.3k55 gold badges3535 silver badges6060 bronze badges

string maxString = dt.AsEnumerable()
 .Select(row => row[mycolumn].ToString())
 .OrderByDescending(st => st.Length).FirstOrDefault();

var row = dt.AsEnumerable().MaxBy(r => r[mycolumn].ToString().Length);

share|improve this answer

edited Apr 15 at 14:48

answered Apr 15 at 7:20

Gilad GreenGilad Green

31.3k55 gold badges3535 silver badges6060 bronze badges

answered Apr 15 at 7:20

Gilad GreenGilad Green

31.3k55 gold badges3535 silver badges6060 bronze badges

answered Apr 15 at 7:20

Gilad GreenGilad Green

31.3k55 gold badges3535 silver badges6060 bronze badges

15

You are looking for ArgMax - a value such that it has max value of some kind of property. Standard Linq doesn't provide ArgMax but you can implement it via Aggregate (i.e. get a single value from a sequence):

 string maxString = dt
 .AsEnumerable()
 .Select(row => row[mycolumn].ToString())
 .Aggregate((s, a) => a.Length > s.Length ? a : s);

share|improve this answer

edited Apr 15 at 12:36

answered Apr 15 at 7:36

Dmitry BychenkoDmitry Bychenko

122k1515 gold badges115115 silver badges150150 bronze badges

• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  This solution is likely much faster than the accepted answer since it doesn't have to actually sort the list, just iterate it once.
  
  – Marie
  Apr 15 at 13:29
  
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  @Marie yes, I tested, this is the fastest one. Though It differs for 1 second comparing to Gilad Green answer in my test for exporting data into Excel with OpenXML for 320k+ rows and 7 columns.
  
  – Lucy82
  Apr 16 at 7:27
  
  

  
  
  
  

add a comment
 | 

15

You are looking for ArgMax - a value such that it has max value of some kind of property. Standard Linq doesn't provide ArgMax but you can implement it via Aggregate (i.e. get a single value from a sequence):

 string maxString = dt
 .AsEnumerable()
 .Select(row => row[mycolumn].ToString())
 .Aggregate((s, a) => a.Length > s.Length ? a : s);

share|improve this answer

edited Apr 15 at 12:36

answered Apr 15 at 7:36

Dmitry BychenkoDmitry Bychenko

122k1515 gold badges115115 silver badges150150 bronze badges

• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  This solution is likely much faster than the accepted answer since it doesn't have to actually sort the list, just iterate it once.
  
  – Marie
  Apr 15 at 13:29
  
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  @Marie yes, I tested, this is the fastest one. Though It differs for 1 second comparing to Gilad Green answer in my test for exporting data into Excel with OpenXML for 320k+ rows and 7 columns.
  
  – Lucy82
  Apr 16 at 7:27
  
  

  
  
  
  

add a comment
 | 

You are looking for ArgMax - a value such that it has max value of some kind of property. Standard Linq doesn't provide ArgMax but you can implement it via Aggregate (i.e. get a single value from a sequence):

 string maxString = dt
 .AsEnumerable()
 .Select(row => row[mycolumn].ToString())
 .Aggregate((s, a) => a.Length > s.Length ? a : s);

share|improve this answer

edited Apr 15 at 12:36

answered Apr 15 at 7:36

Dmitry BychenkoDmitry Bychenko

122k1515 gold badges115115 silver badges150150 bronze badges

 string maxString = dt
 .AsEnumerable()
 .Select(row => row[mycolumn].ToString())
 .Aggregate((s, a) => a.Length > s.Length ? a : s);

share|improve this answer

edited Apr 15 at 12:36

answered Apr 15 at 7:36

Dmitry BychenkoDmitry Bychenko

122k1515 gold badges115115 silver badges150150 bronze badges

answered Apr 15 at 7:36

Dmitry BychenkoDmitry Bychenko

122k1515 gold badges115115 silver badges150150 bronze badges

answered Apr 15 at 7:36

Dmitry BychenkoDmitry Bychenko

122k1515 gold badges115115 silver badges150150 bronze badges

3

First of all do not use AsEnumerable right after dt..
Write somehow like this:

dt.OrderByDescending(row => row[mycolumn].Length).First();

share|improve this answer

answered Apr 15 at 8:09

NoImaginationNoImagination

17811 silver badge77 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  AsEnumerable shouldn't be used because it transfers calculations to app memory, when my example forces it to perform calculations at sql server. When all calculations done First() transfers the result to app memory. Try my example and tell me if it works, ok?
  
  – NoImagination
  Apr 15 at 8:38
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @Lucy82, well i checked my example and it works perfectly :). But as people above noticed it would be much better to find Max value by aggregation function. It requires just 1 cycle when OrderBy sorts.
  
  – NoImagination
  Apr 15 at 12:39
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @Lucy82 Neither the accepted, nor Dmitry's, answer would be good for large datasets that are persisted in a database. Ie. if dt is a table in a database and contains thousands of rows the other answers would first fetch all those rows and then do the sorting to get the max value.
  
  – Taemyr
  Apr 15 at 12:44
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @NoImagination I might be wrong but the question isnt tagged entity or anything. Isn't "when my example forces it to perform calculations at sql server" only true if they are using an ORM that supports that functionality?
  
  – Marie
  Apr 15 at 13:31
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @NoImagination It stands to reason that "dt" stands for DataTable (the row[column] part also makes no sense at all for a EF query) which means that leaving the AsEnumerable off simply won't work. It also means that the data is already in memory so really nothing lost there.
  
  – Voo
  Apr 15 at 17:57
  
  

  
  
  
  

 | 
show 5 more comments

3

First of all do not use AsEnumerable right after dt..
Write somehow like this:

dt.OrderByDescending(row => row[mycolumn].Length).First();

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answered Apr 15 at 8:09

NoImaginationNoImagination

17811 silver badge77 bronze badges

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  AsEnumerable shouldn't be used because it transfers calculations to app memory, when my example forces it to perform calculations at sql server. When all calculations done First() transfers the result to app memory. Try my example and tell me if it works, ok?
  
  – NoImagination
  Apr 15 at 8:38
  
  

  
  
  
  


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  @Lucy82, well i checked my example and it works perfectly :). But as people above noticed it would be much better to find Max value by aggregation function. It requires just 1 cycle when OrderBy sorts.
  
  – NoImagination
  Apr 15 at 12:39
  
  

  
  
  
  


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  @Lucy82 Neither the accepted, nor Dmitry's, answer would be good for large datasets that are persisted in a database. Ie. if dt is a table in a database and contains thousands of rows the other answers would first fetch all those rows and then do the sorting to get the max value.
  
  – Taemyr
  Apr 15 at 12:44
  

  
  
  
  


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  @NoImagination I might be wrong but the question isnt tagged entity or anything. Isn't "when my example forces it to perform calculations at sql server" only true if they are using an ORM that supports that functionality?
  
  – Marie
  Apr 15 at 13:31
  

  
  
  
  


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  @NoImagination It stands to reason that "dt" stands for DataTable (the row[column] part also makes no sense at all for a EF query) which means that leaving the AsEnumerable off simply won't work. It also means that the data is already in memory so really nothing lost there.
  
  – Voo
  Apr 15 at 17:57
  
  

  
  
  
  

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show 5 more comments

First of all do not use AsEnumerable right after dt..
Write somehow like this:

dt.OrderByDescending(row => row[mycolumn].Length).First();

share|improve this answer

answered Apr 15 at 8:09

NoImaginationNoImagination

17811 silver badge77 bronze badges

dt.OrderByDescending(row => row[mycolumn].Length).First();

share|improve this answer

answered Apr 15 at 8:09

NoImaginationNoImagination

17811 silver badge77 bronze badges

answered Apr 15 at 8:09

NoImaginationNoImagination

17811 silver badge77 bronze badges

answered Apr 15 at 8:09

NoImaginationNoImagination

17811 silver badge77 bronze badges