Pick top genes

Overview

The topicks library implements a pick_top_genes() function to pick the top genes based on some statistic. The idea is to use this to choose highly variable genes based on their variances (e.g., from scran_variances), or for picking the best markers based on a differential expression statistic (e.g., from scran_markers). This functionality is surprisingly complex when we need to consider ties, absolute bounds, and whether to return a boolean filter or an array of indices.

Quick start

We can obtain an array of booleans indicating whether each gene was picked based on its stats:

#include "topicks/topicks.hpp"
 
std::vector<double> stats(100); // vector of per-gene statistics.
topicks::PickTopGenesOptions<double> opts;
auto filter = topicks::pick_top_genes(
    stats.size(),
    stats.data(),
    10, // number of top genes to pick.
    true, // whether to pick genes with the largest 'stats'.
    opts
);

Alternatively we can obtain an array of integer indices:

auto idx = topicks::pick_top_genes_index(stats.size(), stats.data(), 10, true, opts);

By default, ties at the selection boundary are retained so the actual number of chosen genes may be greater than what was requested. This can be disabled via the PickTopGenesOptions options:

opt.keep_ties = false;

We can also set an absolute bound on the statistic, e.g., to ensure that we never select marker genes with log-fold changes below some threshold:

opt.bound = 0.5;

Check out the reference documentation for more details.

Building projects

CMake with FetchContent

If you're using CMake, you just need to add something like this to your CMakeLists.txt:

include(FetchContent)
 
FetchContent_Declare(
  topicks
  GIT_REPOSITORY https://github.com/libscran/topicks
  GIT_TAG master # or any version of interest
)
 
FetchContent_MakeAvailable(topicks)

Then you can link to topicks to make the headers available during compilation:

# For executables:
target_link_libraries(myexe libscran::topicks)
 
# For libaries
target_link_libraries(mylib INTERFACE libscran::topicks)

CMake with find_package()

find_package(libscran_topicks CONFIG REQUIRED)
target_link_libraries(mylib INTERFACE libscran::topicks)

To install the library, use:

mkdir build && cd build
cmake .. -DTOPICKER_TESTS=OFF
cmake --build . --target install

By default, this will use FetchContent to fetch all external dependencies. If you want to install them manually, use -DTOPICKER_FETCH_EXTERN=OFF. See the tags in extern/CMakeLists.txt to find compatible versions of each dependency.

Manual

If you're not using CMake, the simple approach is to just copy the files in include/ - either directly or with Git submodules - and include their path during compilation with, e.g., GCC's -I. This requires the external dependencies listed in extern/CMakeLists.txt.