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Overview
On this publish we’ll prepare an autoencoder to detect bank card fraud. We may also reveal find out how to prepare Keras fashions within the cloud utilizing CloudML.
The idea of our mannequin would be the Kaggle Credit score Card Fraud Detection dataset, which was collected throughout a analysis collaboration of Worldline and the Machine Studying Group of ULB (Université Libre de Bruxelles) on huge knowledge mining and fraud detection.
The dataset incorporates bank card transactions by European cardholders revamped a two day interval in September 2013. There are 492 frauds out of 284,807 transactions. The dataset is extremely unbalanced, the optimistic class (frauds) account for under 0.172% of all transactions.
Studying the information
After downloading the information from Kaggle, you may learn it in to R with read_csv():
The enter variables encompass solely numerical values that are the results of a PCA transformation. So as to protect confidentiality, no extra details about the unique options was offered. The options V1, …, V28 had been obtained with PCA. There are nonetheless 2 options (Time and Quantity) that weren’t reworked.
Time is the seconds elapsed between every transaction and the primary transaction within the dataset. Quantity is the transaction quantity and could possibly be used for cost-sensitive studying. The Class variable takes worth 1 in case of fraud and 0 in any other case.
Autoencoders
Since solely 0.172% of the observations are frauds, now we have a extremely unbalanced classification downside. With this type of downside, conventional classification approaches normally don’t work very effectively as a result of now we have solely a really small pattern of the rarer class.
An autoencoder is a neural community that’s used to be taught a illustration (encoding) for a set of knowledge, usually for the aim of dimensionality discount. For this downside we’ll prepare an autoencoder to encode non-fraud observations from our coaching set. Since frauds are alleged to have a distinct distribution then regular transactions, we count on that our autoencoder can have increased reconstruction errors on frauds then on regular transactions. Because of this we are able to use the reconstruction error as a amount that signifies if a transaction is fraudulent or not.
If you wish to be taught extra about autoencoders, a great place to begin is that this video from Larochelle on YouTube and Chapter 14 from the Deep Studying e-book by Goodfellow et al.
Visualization
For an autoencoder to work effectively now we have a robust preliminary assumption: that the distribution of variables for regular transactions is completely different from the distribution for fraudulent ones. Let’s make some plots to confirm this. Variables had been reworked to a [0,1] interval for plotting.
We are able to see that distributions of variables for fraudulent transactions are very completely different then from regular ones, apart from the Time variable, which appears to have the very same distribution.
Preprocessing
Earlier than the modeling steps we have to do some preprocessing. We are going to cut up the dataset into prepare and check units after which we’ll Min-max normalize our knowledge (that is accomplished as a result of neural networks work significantly better with small enter values). We may also take away the Time variable because it has the very same distribution for regular and fraudulent transactions.
Based mostly on the Time variable we’ll use the primary 200,000 observations for coaching and the remaining for testing. That is good follow as a result of when utilizing the mannequin we wish to predict future frauds primarily based on transactions that occurred earlier than.
Now let’s work on normalization of inputs. We created 2 features to assist us. The primary one will get descriptive statistics concerning the dataset which might be used for scaling. Then now we have a operate to carry out the min-max scaling. It’s essential to notice that we utilized the identical normalization constants for coaching and check units.
library(purrr)
#' Will get descriptive statistics for each variable within the dataset.
get_desc <- operate(x) {
map(x, ~listing(
min = min(.x),
max = max(.x),
imply = imply(.x),
sd = sd(.x)
))
}
#' Given a dataset and normalization constants it would create a min-max normalized
#' model of the dataset.
normalization_minmax <- operate(x, desc) {
map2_dfc(x, desc, ~(.x - .y$min)/(.y$max - .y$min))
}Now let’s create normalized variations of our datasets. We additionally reworked our knowledge frames to matrices since that is the format anticipated by Keras.
We are going to now outline our mannequin in Keras, a symmetric autoencoder with 4 dense layers.
___________________________________________________________________________________
Layer (sort) Output Form Param #
===================================================================================
dense_1 (Dense) (None, 15) 450
___________________________________________________________________________________
dense_2 (Dense) (None, 10) 160
___________________________________________________________________________________
dense_3 (Dense) (None, 15) 165
___________________________________________________________________________________
dense_4 (Dense) (None, 29) 464
===================================================================================
Complete params: 1,239
Trainable params: 1,239
Non-trainable params: 0
___________________________________________________________________________________We are going to then compile our mannequin, utilizing the imply squared error loss and the Adam optimizer for coaching.
mannequin %>% compile(
loss = "mean_squared_error",
optimizer = "adam"
)Coaching the mannequin
We are able to now prepare our mannequin utilizing the match() operate. Coaching the mannequin is fairly quick (~ 14s per epoch on my laptop computer). We are going to solely feed to our mannequin the observations of regular (non-fraudulent) transactions.
We are going to use callback_model_checkpoint() to be able to save our mannequin after every epoch. By passing the argument save_best_only = TRUE we’ll carry on disk solely the epoch with smallest loss worth on the check set.
We may also use callback_early_stopping() to cease coaching if the validation loss stops lowering for five epochs.
checkpoint <- callback_model_checkpoint(
filepath = "mannequin.hdf5",
save_best_only = TRUE,
interval = 1,
verbose = 1
)
early_stopping <- callback_early_stopping(persistence = 5)
mannequin %>% match(
x = x_train[y_train == 0,],
y = x_train[y_train == 0,],
epochs = 100,
batch_size = 32,
validation_data = listing(x_test[y_test == 0,], x_test[y_test == 0,]),
callbacks = listing(checkpoint, early_stopping)
)Practice on 199615 samples, validate on 84700 samples
Epoch 1/100
199615/199615 [==============================] - 17s 83us/step - loss: 0.0036 - val_loss: 6.8522e-04d from inf to 0.00069, saving mannequin to mannequin.hdf5
Epoch 2/100
199615/199615 [==============================] - 17s 86us/step - loss: 4.7817e-04 - val_loss: 4.7266e-04d from 0.00069 to 0.00047, saving mannequin to mannequin.hdf5
Epoch 3/100
199615/199615 [==============================] - 19s 94us/step - loss: 3.7753e-04 - val_loss: 4.2430e-04d from 0.00047 to 0.00042, saving mannequin to mannequin.hdf5
Epoch 4/100
199615/199615 [==============================] - 19s 94us/step - loss: 3.3937e-04 - val_loss: 4.0299e-04d from 0.00042 to 0.00040, saving mannequin to mannequin.hdf5
Epoch 5/100
199615/199615 [==============================] - 19s 94us/step - loss: 3.2259e-04 - val_loss: 4.0852e-04 enhance
Epoch 6/100
199615/199615 [==============================] - 18s 91us/step - loss: 3.1668e-04 - val_loss: 4.0746e-04 enhance
...After coaching we are able to get the ultimate loss for the check set by utilizing the consider() fucntion.
loss <- consider(mannequin, x = x_test[y_test == 0,], y = x_test[y_test == 0,])
loss loss
0.0003534254 Tuning with CloudML
We might be able to get higher outcomes by tuning our mannequin hyperparameters. We are able to tune, for instance, the normalization operate, the educational price, the activation features and the dimensions of hidden layers. CloudML makes use of Bayesian optimization to tune hyperparameters of fashions as described in this weblog publish.
We are able to use the cloudml package deal to tune our mannequin, however first we have to put together our mission by making a coaching flag for every hyperparameter and a tuning.yml file that may inform CloudML what parameters we wish to tune and the way.
The complete script used for coaching on CloudML may be discovered at https://github.com/dfalbel/fraud-autoencoder-example. An important modifications to the code had been including the coaching flags:
FLAGS <- flags(
flag_string("normalization", "minmax", "One in all minmax, zscore"),
flag_string("activation", "relu", "One in all relu, selu, tanh, sigmoid"),
flag_numeric("learning_rate", 0.001, "Optimizer Studying Price"),
flag_integer("hidden_size", 15, "The hidden layer dimension")
)We then used the FLAGS variable contained in the script to drive the hyperparameters of the mannequin, for instance:
mannequin %>% compile(
optimizer = optimizer_adam(lr = FLAGS$learning_rate),
loss = 'mean_squared_error',
)We additionally created a tuning.yml file describing how hyperparameters must be various throughout coaching, in addition to what metric we wished to optimize (on this case it was the validation loss: val_loss).
tuning.yml
trainingInput:
scaleTier: CUSTOM
masterType: standard_gpu
hyperparameters:
purpose: MINIMIZE
hyperparameterMetricTag: val_loss
maxTrials: 10
maxParallelTrials: 5
params:
- parameterName: normalization
sort: CATEGORICAL
categoricalValues: [zscore, minmax]
- parameterName: activation
sort: CATEGORICAL
categoricalValues: [relu, selu, tanh, sigmoid]
- parameterName: learning_rate
sort: DOUBLE
minValue: 0.000001
maxValue: 0.1
scaleType: UNIT_LOG_SCALE
- parameterName: hidden_size
sort: INTEGER
minValue: 5
maxValue: 50
scaleType: UNIT_LINEAR_SCALEWe describe the kind of machine we wish to use (on this case a standard_gpu occasion), the metric we wish to decrease whereas tuning, and the the utmost variety of trials (i.e. variety of combos of hyperparameters we wish to check). We then specify how we wish to fluctuate every hyperparameter throughout tuning.
You may be taught extra concerning the tuning.yml file on the Tensorflow for R documentation and at Google’s official documentation on CloudML.
Now we’re able to ship the job to Google CloudML. We are able to do that by operating:
library(cloudml)
cloudml_train("prepare.R", config = "tuning.yml")The cloudml package deal takes care of importing the dataset and putting in any R package deal dependencies required to run the script on CloudML. In case you are utilizing RStudio v1.1 or increased, it would additionally let you monitor your job in a background terminal. You can even monitor your job utilizing the Google Cloud Console.
After the job is completed we are able to acquire the job outcomes with:
It will copy the recordsdata from the job with the very best val_loss efficiency on CloudML to your native system and open a report summarizing the coaching run.
Since we used a callback to save lots of mannequin checkpoints throughout coaching, the mannequin file was additionally copied from Google CloudML. Information created throughout coaching are copied to the “runs” subdirectory of the working listing from which cloudml_train() known as. You may decide this listing for the latest run with:
[1] runs/cloudml_2018_01_23_221244595-03You can even listing all earlier runs and their validation losses with:
ls_runs(order = metric_val_loss, lowering = FALSE) run_dir metric_loss metric_val_loss
1 runs/2017-12-09T21-01-11Z 0.2577 0.1482
2 runs/2017-12-09T21-00-11Z 0.2655 0.1505
3 runs/2017-12-09T19-59-44Z 0.2597 0.1402
4 runs/2017-12-09T19-56-48Z 0.2610 0.1459
Use View(ls_runs()) to view all columnsIn our case the job downloaded from CloudML was saved to runs/cloudml_2018_01_23_221244595-03/, so the saved mannequin file is offered at runs/cloudml_2018_01_23_221244595-03/mannequin.hdf5. We are able to now use our tuned mannequin to make predictions.
Making predictions
Now that we educated and tuned our mannequin we’re able to generate predictions with our autoencoder. We have an interest within the MSE for every remark and we count on that observations of fraudulent transactions can have increased MSE’s.
First, let’s load our mannequin.
mannequin <- load_model_hdf5("runs/cloudml_2018_01_23_221244595-03/mannequin.hdf5",
compile = FALSE)Now let’s calculate the MSE for the coaching and check set observations.
An excellent measure of mannequin efficiency in extremely unbalanced datasets is the Space Underneath the ROC Curve (AUC). AUC has a pleasant interpretation for this downside, it’s the likelihood {that a} fraudulent transaction can have increased MSE then a standard one. We are able to calculate this utilizing the Metrics package deal, which implements all kinds of frequent machine studying mannequin efficiency metrics.
[1] 0.9546814
[1] 0.9403554To make use of the mannequin in follow for making predictions we have to discover a threshold (okay) for the MSE, then if if (MSE > okay) we take into account that transaction a fraud (in any other case we take into account it regular). To outline this worth it’s helpful to have a look at precision and recall whereas various the brink (okay).
possible_k <- seq(0, 0.5, size.out = 100)
precision <- sapply(possible_k, operate(okay) {
predicted_class <- as.numeric(mse_test > okay)
sum(predicted_class == 1 & y_test == 1)/sum(predicted_class)
})
qplot(possible_k, precision, geom = "line")
+ labs(x = "Threshold", y = "Precision")
recall <- sapply(possible_k, operate(okay) {
predicted_class <- as.numeric(mse_test > okay)
sum(predicted_class == 1 & y_test == 1)/sum(y_test)
})
qplot(possible_k, recall, geom = "line")
+ labs(x = "Threshold", y = "Recall")
An excellent place to begin could be to decide on the brink with most precision however we might additionally base our resolution on how a lot cash we would lose from fraudulent transactions.
Suppose every guide verification of fraud prices us $1 but when we don’t confirm a transaction and it’s a fraud we’ll lose this transaction quantity. Let’s discover for every threshold worth how a lot cash we might lose.
cost_per_verification <- 1
lost_money <- sapply(possible_k, operate(okay) {
predicted_class <- as.numeric(mse_test > okay)
sum(cost_per_verification * predicted_class + (predicted_class == 0) * y_test * df_test$Quantity)
})
qplot(possible_k, lost_money, geom = "line") + labs(x = "Threshold", y = "Misplaced Cash")
We are able to discover the very best threshold on this case with:
[1] 0.005050505If we would have liked to manually confirm all frauds, it might price us ~$13,000. Utilizing our mannequin we are able to scale back this to ~$2,500.
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