cluster_profiles_mle {BPRMeth} | R Documentation

## Cluster methylation profiles using EM

### Description

General purpose functions for clustering latent profiles for different observation models using maximum likelihood estimation (MLE) and the EM algorithm. Initially, it performs parameter checking, and initializes main parameters, such as mixing proportions, basis function coefficients, then the EM algorithm is applied and finally model selection metrics are calculated, such as BIC and AIC.

### Usage

    cluster_profiles_mle(X, K = 3, model = NULL, basis = NULL,
      H = NULL, pi_k = NULL, lambda = 0.5, beta_dispersion = 5,
      gaussian_sigma = rep(0.2, K), w = NULL, em_max_iter = 50,
      epsilon_conv = 1e-04, opt_method = "CG", opt_itnmax = 50,
      init_opt_itnmax = 30, is_parallel = FALSE, no_cores = NULL,
      is_verbose = FALSE, ...)

### Arguments

`X` | The input data, which has to be a `list` of elements of length N, where each element is an `L X C` matrix, where L are the total number of observations. The first column contains the input observations x (i.e. CpG locations). If "binomial" model then C=3, and 2nd and 3rd columns contain total number of trials and number of successes respectively. If "bernoulli" or "gaussian" model, then C=2 containing the output y (e.g. methylation level). If "beta" model, then C=3, where 2nd column contains output y and 3rd column the dispersion parameter.
`K` | Integer denoting the total number of clusters K.
`model` | Observation model name as character string. It can be either 'bernoulli', 'binomial', 'beta' or 'gaussian'.
`basis` | A 'basis' object. E.g. see `create_basis`. If NULL, will an RBF object will be created.
`H` | Optional, design matrix of the input data X. If NULL, H will be computed inside the function.
`pi_k` | Vector of length K, denoting the mixing proportions.
`lambda` | The complexity penalty coefficient for ridge regression.
`beta_dispersion` | Dispersion parameter, only used for Beta distribution and will be the same for all observations.
`gaussian_sigma` | Initial standard deviation of the noise term, only used when having "gaussian" observation model.
`w` | Optional, an (M+1)xK matrix of the initial parameters, where each column consists of the basis function coefficients for each corresponding cluster k. If NULL, will be assigned with default values.
`em_max_iter` | Integer denoting the maximum number of EM iterations.
`epsilon_conv` | Numeric denoting the convergence threshold for EM.
`opt_method` | The optimization method to be used. See `optim` for possible methods. Default is "CG".
`opt_itnmax` | Optional argument giving the maximum number of iterations for the corresponding method. See `optim` for details.
`init_opt_itnmax` | Optimization iterations for obtaining the initial EM parameter values.
`is_parallel` | Logical, indicating if code should be run in parallel.
`no_cores` | Number of cores to be used, default is max_no_cores - 1.
`is_verbose` | Logical, print results during EM iterations.
`...` | Additional parameters.

### Value

An object of class `cluster_profiles_mle_`"obs_model" with the following elements:

- `W`: An (M+1) X K matrix with the optimized parameter values for each cluster. Each column of the matrix corresponds a different cluster k. M are the number of basis functions.

- `pi_k`: Mixing proportions.

- `r_nk`: An (N X K) responsibility matrix of each observations being explained by a specific cluster.

- `basis`: The basis object.

- `nll`: The negative log likelihood vector.

- `labels`: Cluster assignment labels.

- `bic`: Bayesian Information Criterion metric.

- `aic`: Akaike Information Criterion metric.

- `icl`: Integrated Complete Likelihood criterion metric.

- `gaussian_sigma`: Optimized standard deviation for gaussian observation model.

### Details

The beta regression model is based on alternative parameterization of the beta density in terms of the mean and dispersion parameter: https://cran.r-project.org/web/packages/betareg/. For modelling details for Binomial/Bernoulli observation model check the paper for BPRMeth: https://academic.oup.com/bioinformatics/article/32/17/i405/2450762 .

### Author(s)

C.A.Kapourani C.A.Kapourani@ed.ac.uk

### See Also

`create_basis`, `cluster_profiles_vb` `infer_profiles_vb`, `infer_profiles_mle`, `infer_profiles_gibbs`, `create_region_object`

### Examples

    # Example of optimizing parameters for synthetic data using 3 RBFs

    basis <- create_rbf_object(M=3)
    out <- cluster_profiles_mle(X = binomial_data, model = "binomial",
      basis=basis, em_max_iter = 5, opt_itnmax = 5, init_opt_itnmax=5,
      is_parallel = FALSE)

    #-------------------------------------

    basis <- create_rbf_object(M=3)
    out <- cluster_profiles_mle(X = gaussian_data, model = "gaussian",
      basis=basis, em_max_iter = 5, opt_itnmax = 5, init_opt_itnmax=5,
      is_parallel = FALSE)

[Package BPRMeth version 1.13.0 Index]