AutoEncoder
An S4 Class implementing an Autoencoder
Autoencoders are neural networks that try to reproduce their input. Consider this method unstable, as the internals may still be changed.
funA function that does the embedding and returns a dimRedResult object.
stdparsThe standard parameters for the function.
Dimensionality reduction methods are S4 Classes that either be used
directly, in which case they have to be initialized and a full
list with parameters has to be handed to the @fun()
slot, or the method name be passed to the embed function and
parameters can be given to the ..., in which case
missing parameters will be replaced by the ones in the
@stdpars.
Autoencoder can take the following parameters:
The number of dimensions for reduction.
The number of neurons in the hidden layers, the length specifies the number of layers, the length must be impair, the middle number must be the same as ndim.
The activation functions for the layers, one of "tanh", "sigmoid", "relu", "elu", everything else will silently be ignored and there will be no activation function for the layer.
the coefficient for weight decay, set to 0 if no weight decay desired.
The learning rate for gradient descend
Optional: A list of bits and pieces that define the autoencoder in tensorflow, see details.
Optional: A list of keras layers that define the encoder and decoder, specifying this, will ignore all other topology related variables, see details.
If NA, all data will be used for training, else only a random subset of size batchsize will be used
the number of training steps.
There are several ways to specify an autoencoder, the simplest is to pass the
number of neurons per layer in n_hidden, this must be a vector of
integers of impair length and it must be symmetric and the middle number must
be equal to ndim, For every layer an activation function can be
specified with activation.
For regularization weight decay can be specified by setting
weight_decay > 0.
Currently only a gradient descent optimizer is used, the learning rate can be
specified by setting learning_rate.
The learner can operate on batches if batchsize is not NA.
The number of steps the learner uses is specified using n_steps.
If the model did not converge in the first training phase or training with
different data is desired, the dimRedResult object may be
passed as autoencoder parameter; In this case all topology related
parameters will be ignored.
The encoder and decoder part can be specified using a list of keras
layers. This requires a list with two entries, encoder should contain
a LIST of keras layers WITHOUT the layer_input
that will be concatenated in order to form the encoder part.
decoder should be
defined accordingly, the output of decoder must have the same number
of dimensions as the input data.
The model can be entirely defined in tensorflow, it must contain a list with the following entries:
A tensor that defines the encoder.
A tensor that defines the decoder.
A tensor that defines the reconstruction (encoder + decoder).
A tensor that calculates the loss (network + loss function).
A placeholder that points to the data input of
the network AND the encoder.
A placeholder that points to the input of
the decoder.
A tensorflow Session object that holds
the values of the tensors.
Uses tensorflow as a backend, for details an problems relating tensorflow, see https://tensorflow.rstudio.com.
Other dimensionality reduction methods: DRR-class,
DiffusionMaps-class,
DrL-class, FastICA-class,
FruchtermanReingold-class,
HLLE-class, Isomap-class,
KamadaKawai-class, LLE-class,
MDS-class, NNMF-class,
PCA-class, PCA_L1-class,
UMAP-class,
dimRedMethod-class,
dimRedMethodList, kPCA-class,
nMDS-class, tSNE-class
## Not run:
dat <- loadDataSet("3D S Curve")
## use the S4 Class directly:
autoenc <- AutoEncoder()
emb <- autoenc@fun(dat, autoenc@stdpars)
## simpler, use embed():
emb2 <- embed(dat, "AutoEncoder")
plot(emb, type = "2vars")
samp <- sample(floor(nrow(dat) / 10))
embsamp <- autoenc@fun(dat[samp], autoenc@stdpars)
embother <- embsamp@apply(dat[-samp])
plot(embsamp, type = "2vars")
points(embother@data)
## End(Not run)Please choose more modern alternatives, such as Google Chrome or Mozilla Firefox.