How to indicate population structure in EggLib?

Question

[remi.b.md]

In Python, I am using EggLib. I am trying to calculate Jost's D value per SNP found in a VCF file.

Data

Data is here in VCF format. The data set is small, there are 2 populations, 100 individuals per population and 6 SNPs (all on chromosome 1).

Each individual is named Pp.Ii, where p is the population index it belongs to and i is the individual index.

Issue

I fail to understand the format of the Structure object explained here on the EggLib website. I suppose my misunderstanding is due to the fact that the example refers to a FASTA file while I am using a VCF file and I fail to extend the logic of the Structure object to my case.

Code

### Read the vcf file ###
vcf = egglib.io.VcfParser("MyData.vcf") 

### Create the `Structure` object ###
# Dictionary for a given cluster. There is only one cluster.
dcluster = {}            
# Loop through each population 
for popIndex in [0,1]:  
    # dictionnary for a given population. There are two populations
    dpop = {}            
    # Loop through each individual
    for IndIndex in range(popIndex * 100,(popIndex + 1) * 100):     
            # A single list to define an individual
        dpop[IndIndex] = [IndIndex*2, IndIndex*2 + 1]
    dcluster[popIndex] = dpop

Structure = {0: dcluster}

### Define the population structure ###
egglib.stats.make_structure(Structure, None) 

### Configurate the 'ComputeStats' object ###
cs = egglib.stats.ComputeStats()
cs.configure(only_diallelic=False)
cs.add_stats('Dj') # Jost's D

### Isolate a SNP ###
vcf.next()
site = egglib.stats.site_from_vcf(vcf)

### Calculate Jost's D ###
cs.process_site(site, struct=Structure)

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Library/Python/2.7/site-packages/egglib/stats/_cstats.py", line 431, in process_site
    self._frq.process_site(site, struct=struct)
  File "/Library/Python/2.7/site-packages/egglib/stats/_freq.py", line 159, in process_site
    if sum(struct) != site._obj.get_ning(): raise ValueError, 'invalid structure (sample size is required to match)'
ValueError: invalid structure (sample size is required to match)

Answer 1

[remi.b.md]

There are two errors

First error

The function make_structure returns the Structure object but does not save it within stats. You therefore have to save this output.

Structure = egglib.stats.make_structure(struct, None)

Second error

The Structure object must designate haploids. Therefore, create the dictionary as

dcluster = {}            
for popIndex in [0,1]:  
    dpop = {}            
    for IndIndex in range(popIndex * 100,(popIndex + 1) * 100):     
        dpop[IndIndex] = [IndIndex]
    dcluster[popIndex] = dpop

struct = {0: dcluster}