An analyst wants the proportion of surge days within each sensor flag group, so that the proportions in each group add to 1. The analyst runs the code below and reports: “Only 15% of flagged days are surge days, compared with 10% of Normal days, so the flag barely matters.” Explain what has gone wrong in the code and describe how it should be changed. Then comment on the analyst's conclusion.

days |>
  count(sensor_flag, surge) |>
  mutate(prop = n / sum(n))

# A tibble: 4 × 4
  sensor_flag surge     n  prop
  <chr>       <chr> <int> <dbl>
1 High        No       36  0.15
2 High        Yes      36  0.15
3 Normal      No      144   0.6
4 Normal      Yes      24   0.1