cum_prod
Joram Mutenge
2025-10-27
Probabilities are all around us, and if you work in the data field, you’re bound to encounter them. For example, what are the chances that you’ll get into Harvard, become a billionaire, or even better, get into Harvard and become a billionaire? Below is a dataframe showing the chances (probabilities) of each event happening to you.
| Event | Chance |
|---|---|
| str | f64 |
| "Get into Harvard" | 0.04 |
| "Become billionaire" | 0.5 |
| "Be happily married" | 0.12 |
| "Die a hero" | 0.02 |
To determine the chance of all four events happening to you, use the Polars expression cum_prod like this:
| Event | Chance | All_Happening |
|---|---|---|
| str | f64 | f64 |
| "Get into Harvard" | 0.04 | 0.04 |
| "Become billionaire" | 0.5 | 0.02 |
| "Be happily married" | 0.12 | 0.0024 |
| "Die a hero" | 0.02 | 0.000048 |
The last value in All_Happening represents the chance of all events happening. It turns out that your chance of getting into Harvard, becoming a billionaire, being happily married, and dying a hero is 1 in 21 thousand!
The 1 in 21 thousand chance is not indicative of real-life odds. It’s based on fictitious values in the dataframe.
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