Random Number Output Based On Probability Distribution of Outputs I Want

For each position in a wave I want to assign it a number - 1, 2 or 3 based on a number generator outputting 1, 2 or 3. I need to specify the probability that the number generator will create 1, 2 or 3. For example 10% chance of a 1, 30% chance of a 2 and 60% chance of a 3. I can't figure out how to code this. Any help would be greatly appreciated.

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