assess_missing_data_pca: Vizualise how missing data thresholds affect sample clustering
Description
This function can be run in two ways: 1) Without 'thresholds' specified. This will run a PCA
for the input vcf without filtering, and visualize the clustering of samples in two-dimensional
space, coloring each sample according to a priori population assignment given in the popmap.
2) With 'thresholds' specified. This will filter your input vcf file to the specified
missing data thresholds, and run a PCA for each filtering iteration.
For each iteration, a 2D plot will be output showing clustering according to the
specified popmap. This option is ideal for assessing the effects of missing data
on clustering patterns.