I ran into this kind of problem in my projects and I want to see if there more ways to solve it.
EXAMPLE There is some data about apples and pears and the features are dominant color (red, green) and weight in grams. Some apples and pears in the data are missing the color. I know that I can just ignore and remove those apples and pears but is there another way to solve this problem? Since the data for the color is discrete, one or the other, and not continuous, I can't just plug in the median or average color of the other apples and pears. Let's also say that I can't assume or make educated guesses from the data. How should I solve this problem without removing data?