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java efficient de-duplication


java efficient de-duplication

By : user3849102
Date : October 23 2020, 11:12 PM
With these it helps Insane number of rows Use Map&Reduce framework (e.g. Hadoop). This is a full-blown distributed computing so it's an overkill unless you have TBs of data though. ( j/k :) ) Unable to fit all rows in memory Even the result won't fit : Use merge sort, persisting intermediate data to disk. As you merge, you can discard duplicates (probably this sample helps). This can be multi-threaded if you want. The results will fit : Instead of reading everything in-memory and then put it in a HashSet (see below), you can use a line iterator or something and keep adding to this HashSet. You can use ConcurrentHashMap and use more than one thread to read files and add to this Map. Another multi-threaded option is to use ConcurrentSkipListSet. In this case, you will implement compareTo() instead of equals()/hashCode() (compareTo()==0 means duplicate) and keep adding to this SortedSet. Fits in memory Design an object that holds your data, implement a good equals()/hashCode() method and put them all in a HashSet. Or use the methods given above (you probably don't want to persist to disk though).
Oh and if I were you, I will put the unique constraint on the DB anyways...
code :


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Is there a more efficient approach than C# Action delegates for avoiding this code duplication?

Is there a more efficient approach than C# Action delegates for avoiding this code duplication?


By : AlexFrom1990
Date : March 29 2020, 07:55 AM
will be helpful for those in need You could pass a parameter to the method and do A or B depending on the parameter.
I don't like it but I'm just saying it could be done. I actually prefer the Action way.
In C#, how to iterate through collections more efficient and remove code duplication?

In C#, how to iterate through collections more efficient and remove code duplication?


By : user3556193
Date : March 29 2020, 07:55 AM
seems to work fine It would be better to have a way to iterate the keys you want to look up instead. Your current algorithm is iterating over all the key value pairs in AllElements and for each one it's doing a Contains on the settings.RepositoryIds which is a linear search. So the complexity is O(mn) where m is the number of repository ids and n is the number of items in the dictionary. That's worse than the fact that you're running it twice. Instead if you iterate the ids and look them up in the dictionary the complexity will be O(m) because a dictionary lookup runs in constant time.
code :
public Data GetData(DataSettings settings)
{
    return GetData(settings.RepositoryIds);
}

private Data GetData(IEnumerable<Guid> keys)
{
    var item = new Data();

    foreach(var key in keys)
    {
        IRepository value = null;
        if(_provider.AllElements.TryGetValue(key, out value))
        {
            if(value is IA)
                data.ACollection.Add(MakeAItem(value));
            if(value is IB)
                data.BCollection.Add(MakeBItem(value));
        }
    }

    return item;
}
Android: Item Duplication with RecyclerView & CardView - How do I stop the duplication?

Android: Item Duplication with RecyclerView & CardView - How do I stop the duplication?


By : Frances C Harrison
Date : March 29 2020, 07:55 AM
I wish this helpful for you I am using a RecyclerView with a CardView within a TabLayout. The RecyclerView will duplicate the cards on my first tab if I scroll up and down after swiping to a different tab and returning to the first tab. How do I go about preventing the duplication? I will post pastebin links to the rest of the code in the comments of the post. , if i got it correct than try to put it into populateData()
code :
if(data!=null) data.clear();
C# Efficient de-duplication of single Datatable column's data

C# Efficient de-duplication of single Datatable column's data


By : Stefan
Date : March 29 2020, 07:55 AM
help you fix your problem I have a Datatable with some data, example as below, and need to de-duplicate any names in the names field by appending [1], [2] etc. , Here is one approach
code :
DataTable table = new DataTable();
//test data
table.Columns.Add("Name");
table.Columns.Add("X", typeof(int));
table.Rows.Add(new object[] { "john", 10 });
table.Rows.Add(new object[] { "paul", 44 });
table.Rows.Add(new object[] { "ringo", 312 });
table.Rows.Add(new object[] { "george", 30 });
table.Rows.Add(new object[] { "john", 100 });
table.Rows.Add(new object[] { "paul", 443 });

//converting DataTable to enumerable collection of rows and then grouping by name, 
//skipping groups with only one row(such as george or ringo)
var groupedData = table.AsEnumerable().GroupBy(row => row[0].ToString()).Where(g => g.Count() > 1);

//iterate through each group of <string, DataRow>
foreach (var group in groupedData)
{
    int counter = 1; //counter for "[x]" suffix
    //iterate through all rows under one name, eg. John
    foreach (var groupedItem in group)
    {
        //add [x] 
        groupedItem[0] = string.Format("{0} [{1}]", group.Key, counter);
        counter++;
    }
}
Most efficient way to prevent code duplication when sending errors in express

Most efficient way to prevent code duplication when sending errors in express


By : Naeem Gaming
Date : March 29 2020, 07:55 AM
Any of those help I am writing a sign-in function with my express app and do not like the fact that in the callback chain, lots of res.status(500).send(body) are duplicated: , I would rewrite your code like this, where we only have one .catch
code :
router.post('/login', (req, res) => {

    User.findOne({  where: { username: req.body.username }})
        .then(user => {

            if (!user) // If we can't even find a user with that username
                return Promise.reject(true); // You should probably return an Error

            return User.verifyPassword(req.body.password, user)

        })
        .then((verified) => {

            if (!verified) // If password entered does not match user password 
                return Promise.reject(true); // You should probably return an Error

            let signedToken = jwt.sign({
                    user: user.id
                },
                'secret', {
                    expiresIn: 24 * 60 * 60
                }
            );

            res.status(200).send({
                token: signedToken,
                userId: user.id,
                username: user.username
            });

        }).catch(error => {

            // If the db query to find a user explodes
            // If we can't even find a user with that username
            // If password entered does not match user password             

            // You could throw different errors and handle
            // all of them differently here
            res.status(500).send({
                error: error
            });
        });
});
router.post('/login', async(req, res) => {

    try {

        const user = await User.findOne({   where: { username: req.body.username }});

        if (!user) // If we can't even find a user with that username
            throw new Error('Invalid username');

        const verified = await User.verifyPassword(req.body.password, user)

        if (!verified) // If password entered does not match user password 
            throw new Error('Invalid password');

        let signedToken = jwt.sign({
                user: user.id
            },
            'secret', {
                expiresIn: 24 * 60 * 60
            }
        );

        res.status(200).send({
            token: signedToken,
            userId: user.id,
            username: user.username
        });

    } catch(error) {

        // If the db query to find a user explodes
        // If we can't even find a user with that username
        // If password entered does not match user password             
        res.status(500).send({
            error: error.message
        });

    }

});
class Unauthorized extends Error {

    constructor(message) {
        super(message);     
        this.name = 'UnauthorizedError';
        this.statusCode = 401
    }
}

class BadRequest extends Error {

    constructor(message) {
        super(message);     
        this.name = 'BadRequestError';
        this.statusCode = 400
    }
}

/** more errors... **/

module.exports = {
    Unauthorized,
    BadRequest
};
const { Unauthorized } = require('./errors');
/* ... */

try {

    /* ... */
    if (!verified) // Some people may say 422 status code... 
        throw new Unauthorized('Invalid password');

    /* ... */
} catch(error) {

    res.status(error.statusCode || 500).send({
        error: error.message
    });

}
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