Tweak usage when there is only one input VCF

[MarieLataretu]

Hi @jonas-fuchs, thanks for this tool :)

I tested virHEAT on one sample with the default parameters and run into the error, that there is nothing to plot:

virheat vcf out -l $LEN # only one file in the vcf folder
Frequency array seems to be empty. There is nothing to plot.

At first, I thought that my VCF file has an incompatible format. But actually, delete_common_mutations removes all mutations and delete is true by default:

virHEAT/virheat/command.py

Lines 160 to 161 in 07e59b3

	if args.delete:
	frequency_array = data_prep.delete_common_mutations(frequency_array, unique_mutations)

It perfectly works with one sample and --no-delete!

I think it would be nice to warn the user (and suggest using --no-delete) or skip delete_common_mutations (even if delete is true), if there is only one input VCF.

[jonas-fuchs]

Thanks for the feedback! I will do this in the next update. Might switch the default just to 'no-delete' or ignore it if just one sample is used 👍👍👍