I have got a List of strings like:
String1
String1.String2
String1.String2.String3
Other1
Other1.Other2
Test1
Stuff1.Stuff1
Text1.Text2.Text3
Folder1.Folder2.FolderA
Folder1.Folder2.FolderB
Folder1.Folder2.FolderB.FolderC
Now I would like to group this into:
String1.String2.String3
Other1.Other2
Test1
Stuff1.Stuff1
Text1.Text2.Text3
Folder1.Folder2.FolderA
Folder1.Folder2.FolderB.FolderC
If
"String1" is in the next item "String1.String2" I will ignore the first one
and if the second item is in the third I will only take the third "String1.String2.String3"
and so on (n items). The string is structured like a node/path and could be split by a dot.
As you can see for the Folder example Folder2 has got two different Subfolder items so I would need both strings.
Do you know how to handle this with Linq? I would prefer VB.Net but C# is also ok.
Regards Athu
Dim r = input.Where(Function(e, i) i = input.Count - 1 OrElse Not input(i + 1).StartsWith(e + ".")).ToList()
Condition within Where method checks if element is last from input or is not followed by element, that contains current one.
That solution uses the fact, that input is List(Of String), so Count and input(i+1) are available on O(1) time.
LINQ isn't really the correct approach here, because you need to access more than one item at a time.
I would go with something like this:
public static IEnumerable<string> Filter(this IEnumerable<string> source)
{
string previous = null;
foreach(var current in source)
{
if(previous != null && !current.Contains(previous))
yield return previous;
previous = current;
}
yield return previous;
}
Usage:
var result = strings.Filter();
Pretty simple one. Try this:
var lst = new List<string> { /*...*/ };
var sorted =
from item in lst
where lst.Last() == item || !lst[lst.IndexOf(item) + 1].Contains(item)
select item;
the following simple line can do the trick, I'm not sure about the performance cost through
List<string> someStuff = new List<string>();
//Code to the strings here, code not added for brewity
IEnumerable<string> result = someStuff.Where(s => someStuff.Count(x => x.StartsWith(s)) == 1);
Related
The question is:
Given a list of String, find a specific string in the list and return
its index in the ordered list of String sorted by mergesort. There are
two cases:
The string is in the list, return the index it should be in, in the ordered list.
The String is NOT in the list, return the index it is supposed to be in, in the ordered list.
Here is my my code, I assume that the given list is already ordered.
For 2nd case, how do I use mergesort to find the supposed index? I would appreciate some clues.
I was thinking to get a copy of the original list first, sort it, and get the index of the string in the copy list. Here I got stuck... do I use mergesort again to get the index of non-existing string in the copy list?
public static int BSearch(List<String> s, String a) {
int size = s.size();
int half = size / 2;
int index = 0;
// base case?
if (half == 0) {
if (s.get(half) == a) {
return index;
} else {
return index + 1;
}
}
// with String a
if (s.contains(a)) {
// on the right
if (s.indexOf(s) > half) {
List<String> rightHalf = s.subList(half + 1, size);
index += half;
return BSearch(rightHalf, a);
} else {
// one the left
List<String> leftHalf = s.subList(0, half - 1);
index += half;
return BSearch(leftHalf, a);
}
}
return index;
}
When I run this code, the index is not updated. I wonder what is wrong here. I only get 0 or 1 when I test the code even with the string in the list.
Your code only returns 0 or 1 because you don't keep track of your index for each recursive call, instead of resetting to 0 each time. Also, to find where the non-existent element should be, consider the list {0,2,3,5,6}. If we were to run a binary search to look for 4 here, it should stop at the index where element 5 is. Hope that's enough to get you started!
I have a string.
string str = "TTFTTFFTTTTF";
How can I break this string and add character ","?
result should be- TTF,TTF,FTT,TTF
You could use String.Join after you've grouped by 3-chars:
var groups = str.Select((c, ix) => new { Char = c, Index = ix })
.GroupBy(x => x.Index / 3)
.Select(g => String.Concat(g.Select(x => x.Char)));
string result = string.Join(",", groups);
Since you're new to programming. That's a LINQ query so you need to add using System.Linq to the top of your code file.
The Select extension method creates an anonymous type containing the char and the index of each char.
GroupBy groups them by the result of index / 3 which is an integer division that truncates decimal places. That's why you create groups of three.
String.Concat creates a string from the 3 characters.
String.Join concatenates them and inserts a comma delimiter between each.
Here is a really simple solution using StringBuilder
var stringBuilder = new StringBuilder();
for (int i = 0; i < str.Length; i += 3)
{
stringBuilder.AppendFormat("{0},", str.Substring(i, 3));
}
stringBuilder.Length -= 1;
str = stringBuilder.ToString();
I'm not sure if the following is better.
stringBuilder.Append(str.Substring(i, 3)).Append(',');
I would suggest to avoid LINQ in this case as it will perform a lot more operations and this is a fairly simple task.
You can use insert
Insert places one string into another. This forms a new string in your C# program. We use the string Insert method to place one string in the middle of another one—or at any other position.
Tip 1:
We can insert one string at any index into another. IndexOf can return a suitable index.
Tip 2:
Insert can be used to concatenate strings. But this is less efficient—concat, as with + is faster.
for(int i=3;i<=str.Length - 1;i+=4)
{
str=str.Insert(i,",");
}
I'm new to coding.
How do I return a false if there is a string being added that's already in the arraylist?
For example, if you have a list of dog names in the class and you add new dog names in the list, but don't add it when the same dog name was already in the list?
The Solution:
You could use a for statement to iterate through your array list:
public static bool checkArray(string dogName)
{
for int i=0; i<arrayName.Length; i++) // basic for loop to go through whole array
{
if (arrayName[i] == dogName) //checks if array value at index i is the dog's name
{
return true; //if it is, return true
}
}
return false; //gone through whole array, not found so return false
}
This means you can call your method via
string Name = "myDogsName";
bool isAlreadyPresent = checkArray(Name);
Note
This is written in C#, and so other coding languages will slightly
differ in their syntax.
isAlreadyPresent will then contain a bool value if the dog is
present or not
I have written this (for learning purposes) in (possibly) an
inefficient way, but should allow you to understand what is happening
at each stage.
the i++
The i++ may confuse new programmers, but effectively it is the same as writing
i = i + 1;
This also works for i--;
i = i - 1;
Or even i*=2;
i = i * 2;
I would like to find the second to the last item in a list. One article came up with the search terms I used and they suggested getting the index of the last element then backing up one step. Is this really the way to do it....? Seems kinda kludgy / hard coded. Perhaps I'm being too paranoid??
int _lstItemIdx = List<MyObj>.IndexOf(List<MyObj>.Last());
int _sndLstItmIdx = (_lstItemIdx - 1);
Thank You
What's wrong with:
var result = myList[myList.Count-2];
Of course, you need appropriate exception handling in case your list doesn't have 2 elements.
And you can turn it into an extension method:
public static T SecondToLast<T>(this IList<T> source)
{
if (source.Count < 2)
throw new ArgumentException("The list does not have at least 2 elements");
return source[source.Count - 2];
}
i am currently tried to create a small program were the user enter a string in a text area, clicks on a button and the program counts the frequency of different characters in the string and shows the result on another text area.
E.g. Step 1:- User enter:- aaabbbbbbcccdd
Step 2:- User click the button
Step 3:- a 3
b 6
c 3
d 1
This is what I've done so far....
public partial class Form1 : Form
{
Dictionary<string, int> dic = new Dictionary<string, int>();
string s = "";
public Form1()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
s = textBox1.Text;
int count = 0;
for (int i = 0; i < s.Length; i++ )
{
textBox2.Text = Convert.ToString(s[i]);
if (dic.Equals(s[i]))
{
count++;
}
else
{
dic.Add(Convert.ToString(s[i]), count++);
}
}
}
}
}
Any ideas or help how can I countinue because till now the program is giving a run time error when there are same charachter!!
Thank You
var lettersAndCounts = s.GroupBy(c=>c).Select(group => new {
Letter= group.Key,
Count = group.Count()
});
Instead of dic.Equals use dic.ContainsKey. However, i would use this little linq query:
Dictionary<string, int> dict = textBox1.Text
.GroupBy(c => c)
.ToDictionary(g => g.Key.ToString(), g => g.Count());
You are attempting to compare the entire dictionary to a string, that doesn't tell you if there is a key in the dictionary that corresponds to the string. As the dictionary never is equal to the string, your code will always think that it should add a new item even if one already exists, and that is the cause of the runtime error.
Use the ContainsKey method to check if the string exists as a key in the dictionary.
Instead of using a variable count, you would want to increase the numbers in the dictionary, and initialise new items with a count of one:
string key = s[i].ToString();
textBox2.Text = key;
if (dic.ContainsKey(key)) {
dic[key]++;
} else {
dic.Add(key, 1);
}
I'm going to suggest a different and somewhat simpler approach for doing this. Assuming you are using English strings, you can create an array with capacity = 26. Then depending on the character you encounter you would increment the appropriate index in the array. For example, if the character is 'a' increment count at index 0, if the character is 'b' increment the count at index 1, etc...
Your implementation will look something like this:
int count[] = new int [26] {0};
for(int i = 0; i < s.length; i++)
{
count[Char.ToLower(s[i]) - int('a')]++;
}
When this finishes you will have the number of 'a's in count[0] and the number of 'z's in count[25].