---
title: "Introduction to kerastuneR"
output:
  rmarkdown::html_vignette
vignette: >
  %\VignetteIndexEntry{Introduction to kerastuneR}
  %\VignetteEngine{knitr::rmarkdown}
  %\VignetteEncoding{UTF-8}
---

```{r setup, include=FALSE}
knitr::opts_chunk$set(eval = FALSE)
```

## R interface to Keras Tuner

Keras Tuner is a hypertuning framework made for humans. 
It aims at making the life of AI practitioners, hypertuner algorithm creators and model designers as simple as possible by providing them with a clean and easy to use API for hypertuning. Keras Tuner makes moving from a base model to a hypertuned one quick and easy by only requiring you to change a few lines of code.

A hyperparameter tuner for [Keras](https://keras.io/), specifically for ```tf$keras``` with *TensorFlow 2.0*.

Full documentation and tutorials available on the [Keras Tuner website](https://EagerAI.github.io/kerastuneR/).

## Installation

Currently, the package is available on github:

```
devtools::install_github('EagerAI/kerastuneR')
```

Later, you need to install the python module kerastuner:

```
kerastuneR::install_kerastuner(python_path = 'paste python path')
```

## Usage: the basics

Here's how to perform hyperparameter tuning for a single-layer dense neural network using random search.

First, we define a model-building function. It takes an argument ```hp``` from which you can sample hyperparameters, such as ```hp$Int('units', min_value=32L, max_value=512L, step=32L)``` (an integer from a certain range).

Sample data:

```
x_data <- matrix(data = runif(500,0,1),nrow = 50,ncol = 5)
y_data <-  ifelse(runif(50,0,1) > 0.6, 1L,0L) %>% as.matrix()

x_data2 <- matrix(data = runif(500,0,1),nrow = 50,ncol = 5)
y_data2 <-  ifelse(runif(50,0,1) > 0.6, 1L,0L) %>% as.matrix()
```

This function returns a compiled model.

```
library(keras)
library(kerastuneR)
library(dplyr)

build_model = function(hp) {
  
  model = keras_model_sequential()
  model %>% layer_dense(units=hp$Int('units',
                                      min_value=32,
                                      max_value=512,
                                      step=32),
                                      input_shape = ncol(x_data)
                                      activation='relu') %>% 
  layer_dense(units=1, activation='sigmoid') %>% 
  compile(
    optimizer= tf$keras$optimizers$Adam(
      hp$Choice('learning_rate',
                values=c(1e-2, 1e-3, 1e-4))),
    loss='binary_crossentropy',
    metrics='accuracy') 
  return(model)
}
```

Next, instantiate a tuner. You should specify the model-building function, the name of the objective to optimize (whether to minimize or maximize is automatically inferred for built-in metrics), the total number of trials ```(max_trials)``` to test, and the number of models that should be built and fit for each trial ```(executions_per_trial)```.

Available tuners are ```RandomSearch``` and ```Hyperband```.

> Note: the purpose of having multiple executions per trial is to reduce results variance and therefore be able to more accurately assess the performance of a model. If you want to get results faster, you could set executions_per_trial=1 (single round of training for each model configuration).

```
tuner = RandomSearch(
    build_model,
    objective = 'val_accuracy',
    max_trials = 5,
    executions_per_trial = 3,
    directory = 'my_dir',
    project_name = 'helloworld')
```

You can print a summary of the search space:

```
tuner %>% search_summary()
```

Then, start the search for the best hyperparameter configuration. The call to search has the same signature as ```model %>% fit()```. But here instead of ```fit()``` we call ```fit_tuner()```.

```
tuner %>% fit_tuner(x_data,y_data,
                    epochs=5, 
                    validation_data = list(x_data2,y_data2))
```



