7.3 filter

filter() is used to filter rows in a data frame / tibble.

Keep rows if Democratic is found in column party:

name start end party
Eisenhower 1953-01-20 1961-01-20 Republican
Kennedy 1961-01-20 1963-11-22 Democratic
Johnson 1963-11-22 1969-01-20 Democratic
Nixon 1969-01-20 1974-08-09 Republican
Ford 1974-08-09 1977-01-20 Republican
Carter 1977-01-20 1981-01-20 Democratic
Reagan 1981-01-20 1989-01-20 Republican
Bush 1989-01-20 1993-01-20 Republican
Clinton 1993-01-20 2001-01-20 Democratic
Bush 2001-01-20 2009-01-20 Republican
Obama 2009-01-20 2017-01-20 Democratic 
 filter(presidential, 
        party=="Democratic")
## # A tibble: 5 x 4
##   name    start      end        party     
##   <chr>   <date>     <date>     <chr>     
## 1 Kennedy 1961-01-20 1963-11-22 Democratic
## 2 Johnson 1963-11-22 1969-01-20 Democratic
## 3 Carter  1977-01-20 1981-01-20 Democratic
## 4 Clinton 1993-01-20 2001-01-20 Democratic
## 5 Obama   2009-01-20 2017-01-20 Democratic

You can filter using several variables/columns:

filter(presidential, 
       party=="Republican", name=="Bush")

# This implicity uses the "&", i.e. the fact that both conditions have to be TRUE
filter(presidential, 
       party=="Republican" & name=="Bush")

# Any logical operators can be used
filter(presidential, 
       name %in% c("Bush", "Kennedy"))

The same can be used for numerical values: let’s select all rows from table5 where century > 19:

filter(table5,
       century > 19)
## # A tibble: 3 x 4
##   country     century year  rate             
##   <chr>       <chr>   <chr> <chr>            
## 1 Afghanistan 20      00    2666/20595360    
## 2 Brazil      20      00    80488/174504898  
## 3 China       20      00    213766/1280428583

HANDS-ON

Going back to our previously create starwarsBMI data frame:

  • How many characters have a BMI > 30?
  • How many characters have a BMI > 30 AND are Droids (“Droid” in column species)?
  • From the previous selection (BMI > 30 and Droid), select columns BMI, character_name, height and mass, and save in the new object DroidBMI30.
Answer 
# How many characters have a BMI > 30?
filter(starwarsBMI, BMI > 30)

# How many characters have a BMI > 30 AND are Droids ("Droid" in column "species")?
filter(starwarsBMI, BMI > 30 & species=="Droid")
  
# From the previous selection (BMI > 30 and Droid), select columns BMI, character_name, height and mass, and save in the new object DroidBMI30.
DroidBMI30 <- starwarsBMI %>% 
            filter(BMI > 30 & species=="Droid") %>% 
            select(BMI, character_name, height, mass)