Wolfram Function Repository
Instantuse addon functions for the Wolfram Language
Function Repository Resource:
Get the proportion of times that each distinct element appears in a list when evaluated with a given function
ResourceFunction["ProportionsBy"][{e_{1},e_{2},…},f] gives an association whose keys are the distinct values of the f[e_{i}] and whose values give the proportion of times these f[e_{i}] values appear. 

ResourceFunction["ProportionsBy"][f] represents an operator form of ResourceFunction["ProportionsBy"] that can be applied to an expression. 
Determine the proportion of a list of integers that is EvenQ:
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Get the proportion of a list that is PrimeQ:
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Use with an Association:
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Use the operator form of ProportionsBy:
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See how common each character is in a body of text while ignoring case:
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Check for common words:
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Visualize in a WordCloud:
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The result of ProportionsBy is identical to that of Proportions applied to the results of Map:
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Wolfram Language 11.3 (March 2018) or above
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