MauroCerbai

Ma tu lo conosci Kotlin? Vieni a scoprire il linguaggio ad oggetti progettato da JetBrains con due workshop esclusivi organizzati dal GDG Torino!Che tu voglia sviluppare su Android al meglio o scoprire le potenzialità di questo nuovo linguaggio in un contesto inedito, questo è l’evento per te!
Due talk con due speaker d'eccezione: Mercoledì 4 aprile alle 18:30, presso la sede di Leva Engineering in Via Vincenzo Gioberti 18, prenderanno la parola Roberto Orgiu, GDE esperto di sviluppo Android e Roberto Franchini, CTO di Arcade.

https://www.meetup.com/it-IT/GDG-Torino/events/248799142/?eventId=248799142

LIVE ACTION:

Roberto Orgiu:

• extension function
• inline
• reified
• destructuring declarations
• dataclass
• component
• operator
• apply, let, with, run

Roberto Franchini:

• live coding session handling twitter stream & save on OrientDB

FINDVIEWBYID

 mWeatherTextView = (TextView) findViewById(R.id.tv_weather_data);  

READ JSON DATA

 JSONObject weatherdata = new JSONObject (JSONstring);  
 JSONObject weather = weatherdata.getJSONObject("weather");  
 String condition = weather.getString("condition");  

BUILD URI AND CONVERT TO URL

 Uri builturi = Uri.parse(BASE_URL).buildUpon()  
     .appendQueryParameter(QUERY_PARAM, param)  
     .build();  
 URL url = null;  
 try {  
   url = new URL(builturi.toString());  
 } catch (MalformedURLException e) {  
   e.printStackTrace();  
 }  
 return url;  

EXECUTE ASYNCTASK

 new GithubQueryTask().execute(githubSearchUrl);  

ADD MENU IN TOP BAR

 @Override  
 public boolean onCreateOptionsMenu(Menu menu) {  
   MenuInflater inflater = getMenuInflater();  
   inflater.inflate(R.menu.forecast, menu);  
   return true;  
 } 

 @Override  
 public boolean onOptionsItemSelected(MenuItem item) {  
   if (item.getItemId() == R.id.action_refresh) {  
     mWeatherTextView.setText("");  
     loadWeatherData();  
     return true;  
   }  
   return super.onOptionsItemSelected(item);  
 }  

EXPLICIT INTENT

 Intent intent = new Intent(this, SettingsActivity.class);  
 startActivity(intent);  

INTENT FOR EXTERNAL MAP

 Intent intent = new Intent(Intent.ACTION_VIEW);  
 Uri uri = new Uri.Builder().scheme("geo").path("0,0").query("california").build();  
 intent.setData(uri);  
 if (intent.resolveActivity(getPackageManager()) != null) {  
   startActivity(intent);  
 }  

SHARE INTENT

 Intent shareIntent = ShareCompat.IntentBuilder.from(activity)  
  .setType("text/plain")  
  .setText(shareText)  
  .getIntent();  
 if (shareIntent.resolveActivity(getPackageManager()) != null) {  
  startActivity(shareIntent);  
 }  

ITEM IN THE ACTION BAR

 <item  
   android:id="@+id/action_share"  
   android:title="Share"  
   android:orderInCategory="1"  
   app:showAsAction="ifRoom"/>  

ASYNCTASKLOADER

 @Override  
 public Loader<String[]> onCreateLoader(int id, Bundle args) {  
   return new AsyncTaskLoader<String[]>(this) {  
     String[] weatherData = null; //Cache data  
     @Override protected void onStartLoading() {}//Check cache data and show progress bar then forceLoad()  
     @Override public String[] loadInBackground() {}//Get data from prefences or bundle and do network request  
     @Override public void deliverResult(String[] data) {}//save data in cache  
   };  
 }  

USE PREFERENCEFRAGMENT

SHAREDPREFERENCES

 SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(this);  
 sharedPreferences.getBoolean("show_bass", true);  

LISTEN TO SWYPE ON RECYCLEVIEW

 new ItemTouchHelper(new ItemTouchHelper.SimpleCallback(0, ItemTouchHelper.LEFT | ItemTouchHelper.RIGHT) {  
   @Override  
   public boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, RecyclerView.ViewHolder target) {  
     return false;  
   }  
   @Override  
   public void onSwiped(RecyclerView.ViewHolder viewHolder, int swipeDir) {  
     long id = (long) viewHolder.itemView.getTag();  
     removeGuest(id);  
     mAdapter.swapCursor(getAllGuests());  
   }  
 }).attachToRecyclerView(waitlistRecyclerView);  

To resolve this we use the confusion matrix

• recall = how many times you get correctly? (similar to accuracy)

true positive / ( true positive + false negative )

• precision = once predicted x, what is the probability that is really x?

true positive / ( true positive + false positive )

In k-fold cross-validation, the original sample is randomly partitioned into k equal sized subsamples. Of the k subsamples, a single subsample is retained as the validation data for testing the model, and the remaining k − 1 subsamples are used as training data.

• repat k times
• pick 1 block of data as test
• train against the othe k-1 block
• test on testing set
• average final result

PRINCIPAL COMPONENT ANALYSIS

The pca of a dataset is the direction that has the largest variance (variance = spread of data distribution) because it retains the maximum amount of original information. That is true because projecting the original data on the longer axis of the new coordinate system we can have a more spread data value and lose the minimum amount of information possible.

• access latent feature
• dimensionality reduction
• visualize high dimensional data
• reduce noise
• use as preprocessing (reducing input for later algo [ eigenfaces] )

• simplification of models to make them easier to interpret by researchers/users
• shorter training times
• to avoid the curse of dimensionality
• enhanced generalization by reducing overfitting

• Use human intuition
• Code the new feature
• Visualize
• Repeat

Getting rid of a feature (feature selection):

• There are very large number of words that they don’t provide any information to the text (such as a, and, the, etc), they are called stop words and they should be removed before analysis.

• There are many word that  can have multiple “flavors” (like response, unresponsive, respond, etc) so we need to search for the common root of the word and use it as substitute. Those words are prepared by linguistic expert.

• Bag of Words (BoW) is an algorithm that counts how many times a word appears in a document. The text is represented as a bag (multiset) of its words, disregarding grammar and even word order but keeping multiplicity
• Term-frequency-inverse document frequency (TF-IDF) is another way to judge the topic of an article by the words it contains. It measures the number of times that words appear in a given document (term frequency). But because words, such as “and” or “the”, appear frequently in all documents, those are systematically discounted. That’s the inverse-document frequency part. The more documents a word appears in, the less valuable that word is. That’s intended to leave only the frequent AND distinctive words as markers.