Median income calculation from range

median-income-calc.R

library(tidyverse)

income_df <- tibble(income_range = c("0-74", "75-145", "150-325", "325+"),
                    count = c(125, 170, 215, 250)) %>% 
             separate(income_range,
                      into = c("income_min", "income_max"),
                      convert = TRUE)

calc_median_income <- function(df) {
  df %>% 
    arrange(income_min) %>% 
    mutate(cumperc = cumsum(count) / sum(count)) %>% 
    # subset to two rows that are just below cumperc >= 0.5 and above <=0.5
    slice((which.min(cumperc < 0.5) - 1):which.max(cumperc > 0.5)) %>% 
    # do a linear interpolation to find the median minimum to maximum income
    summarise(median_min_income = approx(cumperc, income_min, xout = 0.5)$y,
              median_max_income = approx(cumperc, income_max, xout = 0.5)$y)
}

calc_median_income(income_df)
#> # A tibble: 1 x 2
#>   median_min_income median_max_income
#>               <dbl>             <dbl>
#> 1              105.              216.