how to subset strings

Sometimes you have a column in your data frame that is text, but there is some of it that you don’t need. Lets say your data looks like this…

df <- data.frame(animals = c("this is a bear", "this is a lion", "this is a tiger"))

df

##           animals
## 1  this is a bear
## 2  this is a lion
## 3 this is a tiger

And perhaps only want the animal names… you can use sub_str() from the stringr package to strip out the extra characters. The sub_str() function allows you to specify the position of the character you want to start and end with.

Here I want to start at the 11th character and keep the rest.

Note: spaces are included in your character count.

df_new <- df %>%
  mutate(new_col = str_sub(animals, start = 11))

df_new

##           animals new_col
## 1  this is a bear    bear
## 2  this is a lion    lion
## 3 this is a tiger   tiger

If you wanted to get just the “is a” piece of the string, you can specify both a start and end character.

df_new <- df_new %>%
  mutate(new_col2 = str_sub(animals, start = 6, end = 9))

df_new

##           animals new_col new_col2
## 1  this is a bear    bear     is a
## 2  this is a lion    lion     is a
## 3 this is a tiger   tiger     is a

You can also use - to count backwards from the end. Here I am selecting the last 9 characters.

df_new <- df_new %>%
  mutate(new_col3 = str_sub(animals, start = -9))

df_new

##           animals new_col new_col2  new_col3
## 1  this is a bear    bear     is a is a bear
## 2  this is a lion    lion     is a is a lion
## 3 this is a tiger   tiger     is a s a tiger

Yay- I no longer have to google (IDHTG) how to subset strings with stringr!