scPCA: Sparse Contrastive Principal Component Analysis

In PhilBoileau/scPCA: Sparse Contrastive Principal Component Analysis

Sparse Contrastive Principal Component Analysis

Description

Given target and background data frames or matrices, scPCA will perform the sparse contrastive principal component analysis (scPCA) of the target data for a given number of eigenvectors, a vector of real-valued contrast parameters, and a vector of sparsity inducing penalty terms.

If instead you wish to perform contrastive principal component analysis (cPCA), set the penalties argument to 0. So long as the n_centers parameter is larger than one, the automated hyperparameter tuning heuristic described in \insertCiteboileau2020;textualscPCA is used. Otherwise, the semi-automated approach of \insertCiteabid2018exploring;textualscPCA is used to select the appropriate hyperparameter.

Usage

scPCA(
  target,
  background,
  center = TRUE,
  scale = FALSE,
  n_eigen = 2,
  cv = NULL,
  alg = c("iterative", "var_proj", "rand_var_proj"),
  contrasts = exp(seq(log(0.1), log(1000), length.out = 40)),
  penalties = seq(0.05, 1, length.out = 20),
  clust_method = c("kmeans", "pam", "hclust"),
  n_centers = NULL,
  max_iter = 10,
  linkage_method = "complete",
  n_medoids = 8,
  parallel = FALSE,
  clusters = NULL,
  eigdecomp_tol = 1e-10,
  eigdecomp_iter = 1000,
  scaled_matrix = FALSE
)

Arguments

target	The target (experimental) data set, in a standard format such as a data.frame or matrix. dgCMatrix and DelayedMatrix objects are also supported.
background	The background data set, in a standard format such as a data.frame or matrix. The features must match the features of the target data set. dgCMatrix and DelayedMatrix objects are also supported.
center	A logical indicating whether the target and background data sets' features should be centered to mean zero.
scale	A logical indicating whether the target and background data sets' features should be scaled to unit variance.
n_eigen	A numeric indicating the number of eigenvectors (or (sparse) contrastive components) to be computed. Two eigenvectors are computed by default.
cv	A numeric indicating the number of cross-validation folds to use in choosing the optimal contrastive and penalization parameters from over the grids of contrasts and penalties. Cross-validation is expected to improve the robustness and generalization of the choice of these parameters. However, it increases the time the procedure costs. The default is therefore NULL, corresponding to no cross-validation.
alg	A character indicating the sparse PCA algorithm used to sparsify the contrastive loadings. Currently supports iterative for the \insertCitezou2006sparse;textualscPCA implementation, var_proj for the non-randomized \insertCiteerichson2018sparse;textualscPCA solution, and rand_var_proj for the randomized \insertCiteerichson2018sparse;textualscPCA implementation. Defaults to iterative.
contrasts	A numeric vector of the contrastive parameters. Each element must be a unique, non-negative real number. By default, 40 logarithmically spaced values between 0.1 and 1000 are used. If a single value is provided and penalties is set to 0, then n_centers, clust_method, max_iter, linkage_method, n_medoids, and parallel can be safely ignored.
penalties	A numeric vector of the L1 penalty terms on the loadings. The default is to use 20 equidistant values between 0.05 and 1. If penalties is set to 0, then cPCA is performed in place of scPCA. See contrasts and n_centers arguments for more infotmation.
clust_method	A character specifying the clustering method to use for choosing the optimal contrastive parameter. Currently, this is limited to either k-means, partitioning around medoids (PAM), and hierarchical clustering. The default is k-means clustering.
n_centers	A numeric giving the number of centers to use in the clustering algorithm. If set to 1, cPCA, as first proposed by \insertCiteabid2018exploring;textualscPCA, is performed, regardless of what the penalties argument is set to.
max_iter	A numeric giving the maximum number of iterations to be used in k-means clustering. Defaults to 10.
linkage_method	A character specifying the agglomerative linkage method to be used if clust_method = "hclust". The options are ward.D2, single, complete, average, mcquitty, median, and centroid. The default is complete.
n_medoids	A numeric indicating the number of medoids to consider if n_centers is set to 1 and contrasts is a vector of length 2 or more. The default is 8 medoids.
parallel	A logical indicating whether to invoke parallel processing via the BiocParallel infrastructure. The default is FALSE for sequential evaluation.
clusters	A numeric vector of cluster labels for observations in the target data. Defaults to NULL, but is otherwise used to identify the optimal set of hyperparameters when fitting the scPCA and the automated version of cPCA. If a vector is provided, the n_centers, clust_method, max_iter, linkage_method, and n_medoids arguments can be safely ignored.
eigdecomp_tol	A numeric providing the level of precision used by eigendecompositon calculations. Defaults to 1e-10.
eigdecomp_iter	A numeric indicating the maximum number of interations performed by eigendecompositon calculations. Defaults to 1000.
scaled_matrix	A logical indicating whether to output a ScaledMatrix object. The centering and scaling procedure is delayed until later, permitting more efficient matrix multiplication and row or column sums downstream. However, this comes at the at the cost of numerical precision. Defaults to FALSE.

Value

A list containing the following components:

• rotation: The matrix of variable loadings if n_centers is larger than one. Otherwise, a list of rotation matrices is returned, one for each medoid. The number of medoids is specified by n_medoids.

• x: The rotated data, centred and scaled if requested, multiplied by the rotation matrix if n_centers is larger than one. Otherwise, a list of rotated data matrices is returned, one for each medoid. The number of medoids is specified by n_medoids.

• contrast: The optimal contrastive parameter.

• penalty: The optimal L1 penalty term.

• center: A logical indicating whether the target dataset was centered.

• scale: A logical indicating whether the target dataset was scaled.

References

\insertAllCited

Examples

# perform cPCA on the simulated data set
scPCA(
  target = toy_df[, 1:30],
  background = background_df,
  contrasts = exp(seq(log(0.1), log(100), length.out = 5)),
  penalties = 0,
  n_centers = 4
)

# perform scPCA on the simulated data set
scPCA(
  target = toy_df[, 1:30],
  background = background_df,
  contrasts = exp(seq(log(0.1), log(100), length.out = 5)),
  penalties = seq(0.1, 1, length.out = 3),
  n_centers = 4
)

# perform cPCA on the simulated data set with known clusters
scPCA(
  target = toy_df[, 1:30],
  background = background_df,
  contrasts = exp(seq(log(0.1), log(100), length.out = 5)),
  penalties = 0,
  clusters = toy_df[, 31]
)

# cPCA as implemented in Abid et al.
scPCA(
  target = toy_df[, 1:30],
  background = background_df,
  contrasts = exp(seq(log(0.1), log(100), length.out = 10)),
  penalties = 0,
  n_centers = 1
)

PhilBoileau/scPCA documentation built on Feb. 12, 2025, 3:08 p.m.