How to group by numeric variables in a dataframe and compute percentiles

Roberta_Grouping.R

# install.packages("tidyverse") # If not yet installed, run this
library(tidyverse) # Everything will be don in a tidyverse fashion

# This is the kind of dataframe I think Roberta is dealing with.
# Vitd is an integer
# Age is a numeric
# We first need to cut the numeric age into a factor.
roberta_df <- tibble(
  Age = as.integer(runif(100,10,100)), # Age, as an integer
  Vitd = as.integer(runif(100,80,140)) # Vitd, as an integer
)

# To give a look at the data frame we created execute the following line
# roberta_df %>% View()

# To categorise Vitd for the age groups,
# we group by Age categories,
# and summarise computing medians and quantiles for each Age group
# (we could compute whatever else statistics)
roberta_df %>%
  mutate(Age_category = cut(Age, # We cut the Age
                            breaks=c(0, 55, 65,75,Inf))) %>% # into groups with this boundaries
  group_by(Age_category) %>% # We group by Age class
  summarise(`25%`=quantile(Vitd, probs=0.25), # And compute the 25%
            med=median(Vitd), # median
            `75%`=quantile(Vitd, probs=0.75)) # and 75% percentile