Azure Automated Machine Learning- Part 5

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Azure ML Services has a new component that has been announced a couple of months ago, name Automated Machine Learning. I already start to write about Azure ML Services and Automated ML specifically recently ( which will continue 🙂 ). In Post one to 4 you can find all discussions ( Post 1, Post 2, Post 3, and Post 4).

In this post, I briefly explain the algorithms and pre-process approaches that have been used in Azure Automated ML.

Algorithms 

If you are using Azure Automated ML you can select the prediction tasks ( see below)

Or if you using the Azure Not book and Python for Automated model, you able to choose the prediction task via Python code as below.

No matter what approaches (via Azure NOtebook or Automated ML interface) you are using for choosing the prediction task, there are a list of algorithms that have been applied on the dataset as below table [1]

 

Classification Regression Time Series Forecasting
Logistic Regression Elastic Net Elastic Net
Light GBM Light GBM Light GBM
Gradient Boosting Gradient Boosting Gradient Boosting
Decision Tree Decision Tree Decision Tree
K Nearest Neighbors K Nearest Neighbors K Nearest Neighbors
Linear SVC LARS Lasso LARS Lasso
C-Support Vector Classification (SVC) Stochastic Gradient Descent (SGD) Stochastic Gradient Descent (SGD)
Random Forest Random Forest Random Forest
Extremely Randomized Trees Extremely Randomized Trees Extremely Randomized Trees
Xgboost Xgboost Xgboost
DNN Classifier DNN Regressor DNN Regressor
DNN Linear Classifier Linear Regressor Linear Regressor
Naive Bayes
Stochastic Gradient Descent (SGD)

If you click on each of those algorithms, will see some technical explanation on specific algorithms.

Some of the algorithms can be seen in all three tasks, like KNN or decision tree. If you click on the explanation of these algorithms, you will see how these algorithms can be used for classification and regression approaches.

 

Data preprocessing & featurization

In most machine learning practice, we need to do some pre-process activities such as remove missing values, scaling data, group and binning, and feature selections.

In Automated ML ( wizard) or Azure NOte book ( Python codes), you will able to access standard preprocess and advance preprocess options.

Standard Preprocess 

If you are using Automated ML, by default the standard preprocess will apply. The standard one is limited to the normalizing the data. For most ML algorithms you need to scale data based on the nature of data. One of the below approaches may be used for scaling based on the nature of data.

 

Scaling & normalization Description
StandardScaleWrapper

Standardize features by removing the mean and scaling to unit variance

 

MinMaxScalar

Transforms features by scaling each feature by that column’s minimum and maximum

 

MaxAbsScaler

Scale each feature by its maximum absolute value

 

RobustScalar

This Scaler features by their quantile range

 

PCA

Linear dimensionality reduction using Singular Value Decomposition of the data to project it to a lower-dimensional space

 

TruncatedSVDWrapper

This transformer performs linear dimensionality reduction by means of truncated singular value decomposition (SVD). Contrary to PCA, this estimator does not center the data before computing the singular value decomposition. This means it can work with scipy.sparse matrices efficiently

 

SparseNormalizer

Each sample (that is, each row of the data matrix) with at least one non-zero component is re-scaled independently of other samples so that its norm (l1 or l2) equals one

 

Advance Preprocessing

For, having access to more data preparation, you can choose the preprocess be active wether in Automated ML or Azure Notebook ( Python). In Automated ML, if you choose the Preprocessing option ( as shown below) then you will get a list of preprocessing options.

 

The same in Python code in Azure NOtebook, you will able to access the preprocessing,

need to set the value to
preprocess:bool=True

By activating the preprocess task ( via Python code or via visual interface), below tasks will run automatically apply to your data [2].

Pre Processing steps

Description

Drop high cardinality or no variance features

Drop these from training and validation sets, including features with all values missing, same value across all rows or with extremely high cardinality (for example, hashes, IDs, or GUIDs).

 

Impute missing values

For numerical features, impute with an average of values in the column. For categorical features, impute with most frequent value.

 

Generate additional features

For DateTime features: Year, Month, Day, Day of the week, Day of Year, Quarter, Week of the year, Hour, Minute, Second.

For Text features: Term frequency based on unigrams, bi-grams, and tri-character-grams.

 

Transform and encode

Numeric features with few unique values are transformed into categorical features.

One-hot encoding is performed for low cardinality categorical; for high cardinality, one-hot-hash encoding.

 

Word embeddings

Text feature that converts vectors of text tokens into sentence vectors using a pre-trained model. Each word’s embedding vector in a document is aggregated together to produce a document feature vector.

 

Target encodings

For categorical features, maps each category with the averaged target value for regression problems, and to the class probability for each class for classification problems. Frequency-based weighting and k-fold cross-validation are applied to reduce overfitting of the mapping and noise caused by sparse data categories.

 

Text target encoding

For text input, a stacked linear model with bag-of-words is used to generate the probability of each class.

 

Weight of Evidence (WoE)

Calculates WoE as a measure of the correlation of categorical columns to the target column. It is calculated as the log of the ratio of in-class vs out-of-class probabilities. This step outputs one numerical feature column per class and removes the need to explicitly impute missing values and outlier treatment.

 

Cluster Distance

Trains a k-means clustering model on all numerical columns. Outputs knew features, one new numerical feature per cluster, containing the distance of each sample to the centroid of each cluster.

 

Reference:

[1] https://docs.microsoft.com/en-us/azure/machine-learning/service/how-to-configure-auto-train#data-pre-processing-and-featurization

[2]https://docs.microsoft.com/en-us/azure/machine-learning/service/how-to-create-portal-experiments

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Leila Etaati
Trainer, Consultant, Mentor
Leila is the first Microsoft AI MVP in New Zealand and Australia, She has Ph.D. in Information System from the University Of Auckland. She is the Co-director and data scientist in RADACAD Company with more than 100 clients in around the world. She is the co-organizer of Microsoft Business Intelligence and Power BI Use group (meetup) in Auckland with more than 1200 members, She is the co-organizer of three main conferences in Auckland: SQL Saturday Auckland (2015 till now) with more than 400 registrations, Difinity (2017 till now) with more than 200 registrations and Global AI Bootcamp 2018. She is a Data Scientist, BI Consultant, Trainer, and Speaker. She is a well-known International Speakers to many conferences such as Microsoft ignite, SQL pass, Data Platform Summit, SQL Saturday, Power BI world Tour and so forth in Europe, USA, Asia, Australia, and New Zealand. She has over ten years’ experience working with databases and software systems. She was involved in many large-scale projects for big-sized companies. She also AI and Data Platform Microsoft MVP. Leila is an active Technical Microsoft AI blogger for RADACAD.

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