Use unique to get the sorted unique values of your array and use that as your bins. Note that due to the way histcounts / histogram work with the last bin you need to add an extra bin at the end ( +Inf works):
data = [0 0.1 0.2 0.3 0.1 0.2]
bins = [unique(data) Inf];
h = histcounts(data, bins)
Important: If your data has been generated by some mathematical calculations then there may be some very small differences between your first and second 0.1 that matlab by default does not show. However, unique won't consider them equal. If that is the case, use uniquetol instead. To see what I mean, compare:
>>data = [0.1+0.1+0.1 0.3]
data =
0.3 0.3
>>unique(data)
ans =
0.3 0.3
>>uniquetol(data)
ans =
0.3
