Provide utilities for genotype files

Issue:
https://github.com/genenetwork/gn-gemtext-threads/blob/main/topics/gn1-migration-to-gn2/clustering.gmi

* gn3/db/genotypes.py: New module
* gn3/settings.py: Add new configuration variable
* qtlfilesexport.py: Test out new code

  Add a module containing functions dealing with the genotype files.
  Add a configuration variable to point to the location of the genotype files.

1 files changed, 69 insertions, 0 deletions

diff --git a/gn3/db/genotypes.py b/gn3/db/genotypes.py
new file mode 100644
index 0000000..610ddde
--- /dev/null
+++ b/gn3/db/genotypes.py
@@ -0,0 +1,69 @@
+"""Genotype utilities"""
+
+import os
+import gzip
+from gn3.settings import GENOTYPE_FILES
+
+def build_genotype_file(
+        geno_name: str, base_dir: str = GENOTYPE_FILES,
+        extension: str = "geno"):
+    """Build the absolute path for the genotype file."""
+    return "{}/{}.{}".format(os.path.abspath(base_dir), geno_name, extension)
+
+def load_genotype_samples(genotype_filename: str, file_type: str = "geno"):
+    """
+    Load sample of strains from genotype files.
+
+    DESCRIPTION:
+    Traits can contain a varied number of strains, some of which do not exist in
+    certain genotypes. In order to compute QTLs, GEMMAs, etc, we need to ensure
+    to pick only those strains that exist in the genotype under consideration
+    for the traits used in the computation.
+
+    This function loads a list of samples from the genotype files for use in
+    filtering out unusable strains.
+
+
+    PARAMETERS:
+    genotype_filename: The absolute path to the genotype file to load the
+        samples from.
+    file_type: The type of file. Currently supported values are 'geno' and
+        'plink'.
+    """
+    file_type_fns = {
+        "geno": __load_genotype_samples_from_geno,
+        "plink": __load_genotype_samples_from_plink
+    }
+    return file_type_fns[file_type](genotype_filename)
+
+def __load_genotype_samples_from_geno(genotype_filename: str):
+    """
+    Helper function for `load_genotype_samples` function.
+
+    Loads samples from '.geno' files.
+    """
+    gzipped_filename = "{}.gz".format(genotype_filename)
+    if os.path.isfile(gzipped_filename):
+        genofile = gzip.open(gzipped_filename)
+    else:
+        genofile = open(genotype_filename)
+
+    for row in genofile:
+        line = row.strip()
+        if (not line) or (line.startswith(("#", "@"))):
+            continue
+        break
+
+    headers = line.split("\t")
+    if headers[3] == "Mb":
+        return headers[4:]
+    return headers[3:]
+
+def __load_genotype_samples_from_plink(genotype_filename: str):
+    """
+    Helper function for `load_genotype_samples` function.
+
+    Loads samples from '.plink' files.
+    """
+    genofile = open(genotype_filename)
+    return [line.split(" ")[1] for line in genofile]