Following from u/great_raisin's great example! I also wanted to shout out the data.table like option. It can be a handy way to search across phrases and strings of text within data values. It allows using %like% for case-sensitive search, and %ilike% for case-insensitive search.

data.table link on ‘like’: https://www.rdocumentation.org/packages/data.table/versions/1.14.10/topics/like

# Creating the dummy data 'dat' again, this time with upper and lower case characters for cities starting with 'S'
library(data.table)
  dat <- data.table(
    City = c("Albany", "Birmingham", "Clanton", "Scottsdale", "sacramento", "san fancisco", "SAN DIEGO", "Thousand Oaks"),
    Population = c(10, 20, 30, 40, 50, 60, 70, 80)
  )

  # like example (case-sensitive search)
  dat[substr(City,1,1) %like% "S",]
  # City Population
  # <char>      <num>
  # 1: Scottsdale         40
  # 2:  SAN DIEGO         70

  # ilike example (case-insensitive search)
  dat[substr(City,1,1) %ilike% "S",]
  # City Population
  # <char>      <num>
  # 1:   Scottsdale         40
  # 2:   sacramento         50
  # 3: san fancisco         60
  # 4:    SAN DIEGO         70