Removed iterators allocation during creation of sketches for differential indexes

[colobrodo]

Hi,
I've made some modifications to reduce memory consumption when creating sketches for the differential builder.
More precisely, I made the following modifications:

• Removed iterators allocation (filtered_colors) during sketches construction for differential indexes.
• Added reserve for colors ids vector.
• Changed function signature to accept an index.
• Moved calculation of total load inside the first loop.

[jermp]

Looks good to me, thanks! @colobrodo: have you checked that everything works correctly on the example in the README?
I haven't but will try tomorrow.

I mean, this one:
./fulgor build -l ~/salmonella_4546_filenames.txt -o ~/Salmonella_enterica/salmonella_4546 -k 31 -m 20 -d tmp_dir -g 8 -t 8 --verbose --check --meta --diff

[colobrodo]

Yes, I have tested it, but only with the --diff option and not the --meta option. The rest of the command is the same.
Please let me know if you encounter any issues!

[jermp]

Ok, thanks for confirming. Then try it also on the test files in test_data, just to make sure it correctly handles small collections as well. @Alessio-Campa Have you tried it?

[colobrodo]

Ok, thanks for confirming. Then try it also on the test files in test_data, just to make sure it correctly handles small collections as well.

Yes, after building the differential index for the examples in test_data, as indicated in the readme, I can confirm that it works as expected.