Return array index from a lambda but throws IndexOutOfRangeException
I'm trying to learn how to use lambdas and in this code I'm trying to get index of some value that is available in the array, but it just return for values 5 and 8 fine and for the other values it keeps throwing IndexOutOfRangeException!
int nums = { 2, 3, 5, 8, 9 };
int rez = nums.Where(i => nums[i] == 2).FirstOrDefault();
Console.WriteLine(rez);
Please tell me what would happen to "index" return value while trying to retrieving it?
Thanks in advance.
c# linq lambda return indexoutofboundsexception
edited Nov 25 '18 at 18:14
egor.zhdan
3,53053348
asked Nov 25 '18 at 17:39
imanonamiimanonami
132
|
show 1 more comment
I'm trying to learn how to use lambdas and in this code I'm trying to get index of some value that is available in the array, but it just return for values 5 and 8 fine and for the other values it keeps throwing IndexOutOfRangeException!
int nums = { 2, 3, 5, 8, 9 };
int rez = nums.Where(i => nums[i] == 2).FirstOrDefault();
Console.WriteLine(rez);
Please tell me what would happen to "index" return value while trying to retrieving it?
Thanks in advance.
c# linq lambda return indexoutofboundsexception
edited Nov 25 '18 at 18:14
egor.zhdan
3,53053348
asked Nov 25 '18 at 17:39
imanonamiimanonami
132
Do you understand what the "IndexOutOfRange" execption indicates? It means that theiused innums[i]is not a valid index for thenumarray. Ask yourself this: What is the range of valid indexes for yournumarray?
– elgonzo
Nov 25 '18 at 17:48
Yes of course. in this case for 2 should be 0. Is it out?
– imanonami
Nov 25 '18 at 17:49
Look up the documentation forWhere. It does not do what you think it does... (docs.microsoft.com/en-gb/dotnet/api/…)
– elgonzo
Nov 25 '18 at 17:50
But shouldn't the "i" evaluates to 0?
– imanonami
Nov 25 '18 at 17:51
Again, look up the documentation to know what it does. Do not insist on wild blind guessing...
– elgonzo
Nov 25 '18 at 17:52
|
show 1 more comment
I'm trying to learn how to use lambdas and in this code I'm trying to get index of some value that is available in the array, but it just return for values 5 and 8 fine and for the other values it keeps throwing IndexOutOfRangeException!
int nums = { 2, 3, 5, 8, 9 };
int rez = nums.Where(i => nums[i] == 2).FirstOrDefault();
Console.WriteLine(rez);
Please tell me what would happen to "index" return value while trying to retrieving it?
Thanks in advance.
c# linq lambda return indexoutofboundsexception
edited Nov 25 '18 at 18:14
egor.zhdan
3,53053348
asked Nov 25 '18 at 17:39
imanonamiimanonami
132
I'm trying to learn how to use lambdas and in this code I'm trying to get index of some value that is available in the array, but it just return for values 5 and 8 fine and for the other values it keeps throwing IndexOutOfRangeException!
int nums = { 2, 3, 5, 8, 9 };
int rez = nums.Where(i => nums[i] == 2).FirstOrDefault();
Console.WriteLine(rez);
Please tell me what would happen to "index" return value while trying to retrieving it?
Thanks in advance.
c# linq lambda return indexoutofboundsexception
c# linq lambda return indexoutofboundsexception
edited Nov 25 '18 at 18:14
egor.zhdan
3,53053348
asked Nov 25 '18 at 17:39
imanonamiimanonami
132
edited Nov 25 '18 at 18:14
egor.zhdan
3,53053348
asked Nov 25 '18 at 17:39
imanonamiimanonami
132
edited Nov 25 '18 at 18:14
egor.zhdan
3,53053348
edited Nov 25 '18 at 18:14
egor.zhdan
3,53053348
edited Nov 25 '18 at 18:14
egor.zhdan
3,53053348
3,53053348
asked Nov 25 '18 at 17:39
imanonamiimanonami
132
asked Nov 25 '18 at 17:39
imanonamiimanonami
132
asked Nov 25 '18 at 17:39
imanonamiimanonami
132
132
Do you understand what the "IndexOutOfRange" execption indicates? It means that theiused innums[i]is not a valid index for thenumarray. Ask yourself this: What is the range of valid indexes for yournumarray?
– elgonzo
Nov 25 '18 at 17:48
Yes of course. in this case for 2 should be 0. Is it out?
– imanonami
Nov 25 '18 at 17:49
Look up the documentation forWhere. It does not do what you think it does... (docs.microsoft.com/en-gb/dotnet/api/…)
– elgonzo
Nov 25 '18 at 17:50
But shouldn't the "i" evaluates to 0?
– imanonami
Nov 25 '18 at 17:51
Again, look up the documentation to know what it does. Do not insist on wild blind guessing...
– elgonzo
Nov 25 '18 at 17:52
|
show 1 more comment
Do you understand what the "IndexOutOfRange" execption indicates? It means that theiused innums[i]is not a valid index for thenumarray. Ask yourself this: What is the range of valid indexes for yournumarray?
– elgonzo
Nov 25 '18 at 17:48
Yes of course. in this case for 2 should be 0. Is it out?
– imanonami
Nov 25 '18 at 17:49
Look up the documentation forWhere. It does not do what you think it does... (docs.microsoft.com/en-gb/dotnet/api/…)
– elgonzo
Nov 25 '18 at 17:50
But shouldn't the "i" evaluates to 0?
– imanonami
Nov 25 '18 at 17:51
Again, look up the documentation to know what it does. Do not insist on wild blind guessing...
– elgonzo
Nov 25 '18 at 17:52
Do you understand what the "IndexOutOfRange" execption indicates? It means that the
i used in nums[i] is not a valid index for the num array. Ask yourself this: What is the range of valid indexes for your num array?– elgonzo
Nov 25 '18 at 17:48
Do you understand what the "IndexOutOfRange" execption indicates? It means that the
i used in nums[i] is not a valid index for the num array. Ask yourself this: What is the range of valid indexes for your num array?– elgonzo
Nov 25 '18 at 17:48
Yes of course. in this case for 2 should be 0. Is it out?
– imanonami
Nov 25 '18 at 17:49
Yes of course. in this case for 2 should be 0. Is it out?
– imanonami
Nov 25 '18 at 17:49
Look up the documentation for
Where. It does not do what you think it does... (docs.microsoft.com/en-gb/dotnet/api/…)– elgonzo
Nov 25 '18 at 17:50
Look up the documentation for
Where. It does not do what you think it does... (docs.microsoft.com/en-gb/dotnet/api/…)– elgonzo
Nov 25 '18 at 17:50
But shouldn't the "i" evaluates to 0?
– imanonami
Nov 25 '18 at 17:51
But shouldn't the "i" evaluates to 0?
– imanonami
Nov 25 '18 at 17:51
Again, look up the documentation to know what it does. Do not insist on wild blind guessing...
– elgonzo
Nov 25 '18 at 17:52
Again, look up the documentation to know what it does. Do not insist on wild blind guessing...
– elgonzo
Nov 25 '18 at 17:52
|
show 1 more comment
2 Answers
2
active
oldest
votes
in your lambda expression (i => nums[i] == 2), i would represent the number itself not its index so nums[i] won't work.
You can simply do this using Array.IndexOf():
int rez = Array.IndexOf(nums, 2);
Or if you insist on doing it by Linq (not recommended):
int rez = nums.Select((x, i) => new {x, i}).FirstOrDefault(a => a.x == 2).i;
answered Nov 25 '18 at 18:02
Ashkan Mobayen KhiabaniAshkan Mobayen Khiabani
20.9k1667119
Great Akhkan, could you explain how your Linq works? I mean how for other indexes it work?
– imanonami
Nov 25 '18 at 18:13
@Ashkan you need to add a condition to .FirstOrDefault(n => n.x == 2). Otherwise, you just get the first element.
– Dmitry Stepanov
Nov 25 '18 at 18:16
in(x,i),xis the item itself andiis the index, so theSelect would return:[{x =2, i =0}, {x=3, i= 1}, {x=5, i=2}, ...], soFirstOrDefault(a => a.x == 2)` would mean the item from our new collection where it'sxvalue is2, and after finding itsiproperty would be the index. but it is much slower than indexof, so i reccomand using indexof.
– Ashkan Mobayen Khiabani
Nov 25 '18 at 18:18
@DmitryS Thank you, your suggestion works!
– imanonami
Nov 25 '18 at 18:20
@AshkanMobayenKhiabani Great, I just need to learn for future use of Linq and Lambda
– imanonami
Nov 25 '18 at 18:24
|
show 2 more comments
i in your lambda is an element (and not the index) of the nums array.
So, first i is equal to 2 (the first element of nums). nums[2] != 2, so it goes further.
i is equal to 3 (the second element of nums). nums[3] != 2, so it goes further.
Then, i is equal to 5 (the third element of nums).nums[5] != 2 but your array has 5 elements and the last element has index 4 (because index is zero based). So, when you tried to access nums[5] you get an IndexOutOfRangeException expectedly.
answered Nov 25 '18 at 17:51
Dmitry StepanovDmitry Stepanov
1,1491123
add a comment |
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2 Answers
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in your lambda expression (i => nums[i] == 2), i would represent the number itself not its index so nums[i] won't work.
You can simply do this using Array.IndexOf():
int rez = Array.IndexOf(nums, 2);
Or if you insist on doing it by Linq (not recommended):
int rez = nums.Select((x, i) => new {x, i}).FirstOrDefault(a => a.x == 2).i;
answered Nov 25 '18 at 18:02
Ashkan Mobayen KhiabaniAshkan Mobayen Khiabani
20.9k1667119
Great Akhkan, could you explain how your Linq works? I mean how for other indexes it work?
– imanonami
Nov 25 '18 at 18:13
@Ashkan you need to add a condition to .FirstOrDefault(n => n.x == 2). Otherwise, you just get the first element.
– Dmitry Stepanov
Nov 25 '18 at 18:16
in(x,i),xis the item itself andiis the index, so theSelect would return:[{x =2, i =0}, {x=3, i= 1}, {x=5, i=2}, ...], soFirstOrDefault(a => a.x == 2)` would mean the item from our new collection where it'sxvalue is2, and after finding itsiproperty would be the index. but it is much slower than indexof, so i reccomand using indexof.
– Ashkan Mobayen Khiabani
Nov 25 '18 at 18:18
@DmitryS Thank you, your suggestion works!
– imanonami
Nov 25 '18 at 18:20
@AshkanMobayenKhiabani Great, I just need to learn for future use of Linq and Lambda
– imanonami
Nov 25 '18 at 18:24
|
show 2 more comments
in your lambda expression (i => nums[i] == 2), i would represent the number itself not its index so nums[i] won't work.
You can simply do this using Array.IndexOf():
int rez = Array.IndexOf(nums, 2);
Or if you insist on doing it by Linq (not recommended):
int rez = nums.Select((x, i) => new {x, i}).FirstOrDefault(a => a.x == 2).i;
answered Nov 25 '18 at 18:02
Ashkan Mobayen KhiabaniAshkan Mobayen Khiabani
20.9k1667119
Great Akhkan, could you explain how your Linq works? I mean how for other indexes it work?
– imanonami
Nov 25 '18 at 18:13
@Ashkan you need to add a condition to .FirstOrDefault(n => n.x == 2). Otherwise, you just get the first element.
– Dmitry Stepanov
Nov 25 '18 at 18:16
in(x,i),xis the item itself andiis the index, so theSelect would return:[{x =2, i =0}, {x=3, i= 1}, {x=5, i=2}, ...], soFirstOrDefault(a => a.x == 2)` would mean the item from our new collection where it'sxvalue is2, and after finding itsiproperty would be the index. but it is much slower than indexof, so i reccomand using indexof.
– Ashkan Mobayen Khiabani
Nov 25 '18 at 18:18
@DmitryS Thank you, your suggestion works!
– imanonami
Nov 25 '18 at 18:20
@AshkanMobayenKhiabani Great, I just need to learn for future use of Linq and Lambda
– imanonami
Nov 25 '18 at 18:24
|
show 2 more comments
in your lambda expression (i => nums[i] == 2), i would represent the number itself not its index so nums[i] won't work.
You can simply do this using Array.IndexOf():
int rez = Array.IndexOf(nums, 2);
Or if you insist on doing it by Linq (not recommended):
int rez = nums.Select((x, i) => new {x, i}).FirstOrDefault(a => a.x == 2).i;
answered Nov 25 '18 at 18:02
Ashkan Mobayen KhiabaniAshkan Mobayen Khiabani
20.9k1667119
in your lambda expression (i => nums[i] == 2), i would represent the number itself not its index so nums[i] won't work.
You can simply do this using Array.IndexOf():
int rez = Array.IndexOf(nums, 2);
Or if you insist on doing it by Linq (not recommended):
int rez = nums.Select((x, i) => new {x, i}).FirstOrDefault(a => a.x == 2).i;
answered Nov 25 '18 at 18:02
Ashkan Mobayen KhiabaniAshkan Mobayen Khiabani
20.9k1667119
edited Nov 25 '18 at 18:16
answered Nov 25 '18 at 18:02
Ashkan Mobayen KhiabaniAshkan Mobayen Khiabani
20.9k1667119
answered Nov 25 '18 at 18:02
Ashkan Mobayen KhiabaniAshkan Mobayen Khiabani
20.9k1667119
answered Nov 25 '18 at 18:02
Ashkan Mobayen KhiabaniAshkan Mobayen Khiabani
20.9k1667119
20.9k1667119
Great Akhkan, could you explain how your Linq works? I mean how for other indexes it work?
– imanonami
Nov 25 '18 at 18:13
@Ashkan you need to add a condition to .FirstOrDefault(n => n.x == 2). Otherwise, you just get the first element.
– Dmitry Stepanov
Nov 25 '18 at 18:16
in(x,i),xis the item itself andiis the index, so theSelect would return:[{x =2, i =0}, {x=3, i= 1}, {x=5, i=2}, ...], soFirstOrDefault(a => a.x == 2)` would mean the item from our new collection where it'sxvalue is2, and after finding itsiproperty would be the index. but it is much slower than indexof, so i reccomand using indexof.
– Ashkan Mobayen Khiabani
Nov 25 '18 at 18:18
@DmitryS Thank you, your suggestion works!
– imanonami
Nov 25 '18 at 18:20
@AshkanMobayenKhiabani Great, I just need to learn for future use of Linq and Lambda
– imanonami
Nov 25 '18 at 18:24
|
show 2 more comments
Great Akhkan, could you explain how your Linq works? I mean how for other indexes it work?
– imanonami
Nov 25 '18 at 18:13
@Ashkan you need to add a condition to .FirstOrDefault(n => n.x == 2). Otherwise, you just get the first element.
– Dmitry Stepanov
Nov 25 '18 at 18:16
in(x,i),xis the item itself andiis the index, so theSelect would return:[{x =2, i =0}, {x=3, i= 1}, {x=5, i=2}, ...], soFirstOrDefault(a => a.x == 2)` would mean the item from our new collection where it'sxvalue is2, and after finding itsiproperty would be the index. but it is much slower than indexof, so i reccomand using indexof.
– Ashkan Mobayen Khiabani
Nov 25 '18 at 18:18
@DmitryS Thank you, your suggestion works!
– imanonami
Nov 25 '18 at 18:20
@AshkanMobayenKhiabani Great, I just need to learn for future use of Linq and Lambda
– imanonami
Nov 25 '18 at 18:24
Great Akhkan, could you explain how your Linq works? I mean how for other indexes it work?
– imanonami
Nov 25 '18 at 18:13
Great Akhkan, could you explain how your Linq works? I mean how for other indexes it work?
– imanonami
Nov 25 '18 at 18:13
@Ashkan you need to add a condition to .FirstOrDefault(n => n.x == 2). Otherwise, you just get the first element.
– Dmitry Stepanov
Nov 25 '18 at 18:16
@Ashkan you need to add a condition to .FirstOrDefault(n => n.x == 2). Otherwise, you just get the first element.
– Dmitry Stepanov
Nov 25 '18 at 18:16
in
(x,i), x is the item itself and i is the index, so the Select would return: [{x =2, i =0}, {x=3, i= 1}, {x=5, i=2}, ...], so FirstOrDefault(a => a.x == 2)` would mean the item from our new collection where it's x value is 2, and after finding its i property would be the index. but it is much slower than indexof, so i reccomand using indexof.– Ashkan Mobayen Khiabani
Nov 25 '18 at 18:18
in
(x,i), x is the item itself and i is the index, so the Select would return: [{x =2, i =0}, {x=3, i= 1}, {x=5, i=2}, ...], so FirstOrDefault(a => a.x == 2)` would mean the item from our new collection where it's x value is 2, and after finding its i property would be the index. but it is much slower than indexof, so i reccomand using indexof.– Ashkan Mobayen Khiabani
Nov 25 '18 at 18:18
@DmitryS Thank you, your suggestion works!
– imanonami
Nov 25 '18 at 18:20
@DmitryS Thank you, your suggestion works!
– imanonami
Nov 25 '18 at 18:20
@AshkanMobayenKhiabani Great, I just need to learn for future use of Linq and Lambda
– imanonami
Nov 25 '18 at 18:24
@AshkanMobayenKhiabani Great, I just need to learn for future use of Linq and Lambda
– imanonami
Nov 25 '18 at 18:24
|
show 2 more comments
i in your lambda is an element (and not the index) of the nums array.
So, first i is equal to 2 (the first element of nums). nums[2] != 2, so it goes further.
i is equal to 3 (the second element of nums). nums[3] != 2, so it goes further.
Then, i is equal to 5 (the third element of nums).nums[5] != 2 but your array has 5 elements and the last element has index 4 (because index is zero based). So, when you tried to access nums[5] you get an IndexOutOfRangeException expectedly.
answered Nov 25 '18 at 17:51
Dmitry StepanovDmitry Stepanov
1,1491123
add a comment |
i in your lambda is an element (and not the index) of the nums array.
So, first i is equal to 2 (the first element of nums). nums[2] != 2, so it goes further.
i is equal to 3 (the second element of nums). nums[3] != 2, so it goes further.
Then, i is equal to 5 (the third element of nums).nums[5] != 2 but your array has 5 elements and the last element has index 4 (because index is zero based). So, when you tried to access nums[5] you get an IndexOutOfRangeException expectedly.
answered Nov 25 '18 at 17:51
Dmitry StepanovDmitry Stepanov
1,1491123
add a comment |
i in your lambda is an element (and not the index) of the nums array.
So, first i is equal to 2 (the first element of nums). nums[2] != 2, so it goes further.
i is equal to 3 (the second element of nums). nums[3] != 2, so it goes further.
Then, i is equal to 5 (the third element of nums).nums[5] != 2 but your array has 5 elements and the last element has index 4 (because index is zero based). So, when you tried to access nums[5] you get an IndexOutOfRangeException expectedly.
answered Nov 25 '18 at 17:51
Dmitry StepanovDmitry Stepanov
1,1491123
i in your lambda is an element (and not the index) of the nums array.
So, first i is equal to 2 (the first element of nums). nums[2] != 2, so it goes further.
i is equal to 3 (the second element of nums). nums[3] != 2, so it goes further.
Then, i is equal to 5 (the third element of nums).nums[5] != 2 but your array has 5 elements and the last element has index 4 (because index is zero based). So, when you tried to access nums[5] you get an IndexOutOfRangeException expectedly.
answered Nov 25 '18 at 17:51
Dmitry StepanovDmitry Stepanov
1,1491123
edited Nov 25 '18 at 18:01
answered Nov 25 '18 at 17:51
Dmitry StepanovDmitry Stepanov
1,1491123
answered Nov 25 '18 at 17:51
Dmitry StepanovDmitry Stepanov
1,1491123
answered Nov 25 '18 at 17:51
Dmitry StepanovDmitry Stepanov
1,1491123
1,1491123
add a comment |
add a comment |
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Do you understand what the "IndexOutOfRange" execption indicates? It means that the
iused innums[i]is not a valid index for thenumarray. Ask yourself this: What is the range of valid indexes for yournumarray?– elgonzo
Nov 25 '18 at 17:48
Yes of course. in this case for 2 should be 0. Is it out?
– imanonami
Nov 25 '18 at 17:49
Look up the documentation for
Where. It does not do what you think it does... (docs.microsoft.com/en-gb/dotnet/api/…)– elgonzo
Nov 25 '18 at 17:50
But shouldn't the "i" evaluates to 0?
– imanonami
Nov 25 '18 at 17:51
Again, look up the documentation to know what it does. Do not insist on wild blind guessing...
– elgonzo
Nov 25 '18 at 17:52