Add spike-ins in "exon" length computation.

Also noticed a problem involving MultiIndex
(https://stackoverflow.com/q/48345640/1878788).

libhts/__init__.py

-from .libhts import do_deseq2, gtf_2_genes_exon_lengths, median_ratio_to_pseudo_ref_size_factors, plot_boxplots, plot_counts_distribution, plot_lfc_distribution, plot_MA, plot_norm_correlations, plot_scatter, repeat_bed_2_lengths, size_factor_correlations, status_setter
+from .libhts import do_deseq2, gtf_2_genes_exon_lengths, median_ratio_to_pseudo_ref_size_factors, plot_boxplots, plot_counts_distribution, plot_lfc_distribution, plot_MA, plot_norm_correlations, plot_scatter, repeat_bed_2_lengths, size_factor_correlations, spikein_gtf_2_lengths, status_setter

libhts/libhts.py

@@ -117,7 +117,7 @@ def gtf_2_genes_exon_lengths(gtf_filename):
         gene.set_union_exon_length()
     return pd.DataFrame(pd.Series(
         {gene.gene_id : gene.union_exon_length for gene in genes.values()},
-        name=("union_exon_len",)).rename_axis("gene"))
+        name=("union_exon_len")).rename_axis("gene"))
 
 
 def repeat_bed_2_lengths(repeat_bed):
@@ -144,6 +144,20 @@ def repeat_bed_2_lengths(repeat_bed):
     return pd.DataFrame(lens).assign(gene=repeat_families).groupby("gene").sum()
 
 
+def spikein_gtf_2_lengths(spikein_gtf):
+    """Computes the lengths of spike-ins, grouped by families.
+    Returns a DataFrame associating the summed lengths to the spike-in namse.
+    """
+    spikein_ends = {}
+    with open(spikein_gtf) as gtf_file:
+        for line in gtf_file:
+            fields = line.strip().split("\t")
+            spikein_ends[fields[0]] = int(fields[4])
+    return pd.DataFrame(pd.Series(
+        spikein_ends,
+        name=("union_exon_len")).rename_axis("gene"))
+
+
 def do_deseq2(cond_names, conditions, counts_data,
               formula=None, contrast=None, deseq2_args=None):
     """Runs a DESeq2 differential expression analysis."""
@@ -151,6 +165,7 @@ def do_deseq2(cond_names, conditions, counts_data,
         formula = Formula("~ lib")
     if contrast is None:
         # FIXME: MUT and REF are not defined
+        # Maybe just make (formula and) contrast mandatory
         contrast = StrVector(["lib", MUT, REF])
     if deseq2_args is None:
         deseq2_args = {"betaPrior" : True, "addMLE" : True, "independentFiltering" : True}