59 names, rbind and cbind

Written by Isaac Ehrlich and last updated on 7 October 2021.

59.1 Introduction

For certain tasks, you may need to combine data frames and find information about them.

In this lesson, you will learn how to

• Use names() to find the column names of data frames
• Use rbind() to combine two or more data frames (or matrices) by row
• Use cbind() to combine two or more data frames (or matrices) by column

Prerequisites:

• Understanding how to data frames and their basic principles

59.2 Arguments

59.2.1 names()

The primary purpose of names() is to return the column names of a data frame. The only argument that names() takes is the data frame. colnames() is a similar function which outputs the same information, and works for matrices as well.

head(starwars)
#> # A tibble: 6 × 14
#>   name          height  mass hair_color skin_color eye_color
#>   <chr>          <int> <dbl> <chr>      <chr>      <chr>    
#> 1 Luke Skywalk…    172    77 blond      fair       blue     
#> 2 C-3PO            167    75 <NA>       gold       yellow   
#> 3 R2-D2             96    32 <NA>       white, bl… red      
#> 4 Darth Vader      202   136 none       white      yellow   
#> 5 Leia Organa      150    49 brown      light      brown    
#> 6 Owen Lars        178   120 brown, gr… light      blue     
#> # … with 8 more variables: birth_year <dbl>, sex <chr>,
#> #   gender <chr>, homeworld <chr>, species <chr>,
#> #   films <list>, vehicles <list>, starships <list>
names(starwars)
#>  [1] "name"       "height"     "mass"       "hair_color"
#>  [5] "skin_color" "eye_color"  "birth_year" "sex"       
#>  [9] "gender"     "homeworld"  "species"    "films"     
#> [13] "vehicles"   "starships"
table(colnames(starwars) == names(starwars))
#> 
#> TRUE 
#>   14

Using indexing, names() can also be used to change the column names of a data frame.

# Change the homeworld column name (the tenth column) to home-planet
names(starwars)[10] <- "home-planet"
names(starwars)
#>  [1] "name"        "height"      "mass"        "hair_color" 
#>  [5] "skin_color"  "eye_color"   "birth_year"  "sex"        
#>  [9] "gender"      "home-planet" "species"     "films"      
#> [13] "vehicles"    "starships"

The tidyverse rename() function can also be used to change column names, and avoids indexing by specifying the column to rename, using the syntax new_name = old_name.

# Change the starships column name to spaceships
starwars <- 
  starwars %>% 
  rename(spaceships = starships)
names(starwars)
#>  [1] "name"        "height"      "mass"        "hair_color" 
#>  [5] "skin_color"  "eye_color"   "birth_year"  "sex"        
#>  [9] "gender"      "home-planet" "species"     "films"      
#> [13] "vehicles"    "spaceships"

59.2.2 rbind()

The purpose of rbind() is to combine two (or more) data frames by row. The arguments to rbind() are two (or more) data frames. These data frames must have the same number of columns, and must have the same column names as well. rbind() can also be used to combine matrices which match the same requirements.

letter_df <- data.frame(numbers = 1:26, strings = letters)
words_df <- data.frame(numbers = 27:1006, strings = words)

character_df <- rbind(letter_df, words_df)
names(character_df)
#> [1] "numbers" "strings"
dim(character_df) # shows the number of rows and columns
#> [1] 1006    2

59.2.3 cbind()

The purpose of cbind() is to combine two (or more) data frames by column. The arguments to cbind() are two (or more) data frames. These data frames must have the same number of rows, or the number of rows must be multiples of one another. cbind() can also be used to combine matrices which match the same requirements.

Note, in the case that the number of rows are multiples, the rows in the smaller data frame are repeated so they match the longer data frame.

index_df <- data.frame(numbers = 1:5, letters = c("a", "b", "c", "d", "e"))
names_df <- data.frame(vegetables = c("arugula", "broccoli", "cauliflower", "dill", "endive"),
                       fruits = c("apricot", "banana", "cherry", "date", "elderberry"),
                       flowers = c("aster", "begonia", "crocus", "daffodil", "echium"))

combined_df <- cbind(index_df, names_df)
names(combined_df)
#> [1] "numbers"    "letters"    "vegetables" "fruits"    
#> [5] "flowers"
dim(combined_df) # shows the number of rows and columns
#> [1] 5 5

59.3 Questions and Exercises

59.3.1 Question 1

Using the presidential data frame, save the column names, and then change the name of the second column to inauguration-date.

#> [1] "name"  "start" "end"   "party"

presidential_col_names <- names(presidential)

names(presidential)[2] <- "inauguration-date"

59.3.2 Question 2

59.4 Special Cases & Common Mistakes

The most common error with rbind() and cbind() occurs when the data frames do not meet the requirements (e.g. data frames have different number of columns for rbind() or different number of rows for cbind()). These will result in error messages such as “numbers of columns of arguments do not match” or “arguments imply differing number of rows.”

Similarly, if the names of the columns do not match, rbind() will give a “names do not match previous names” error. You can use names() to check against this error.

59.5 Overview & Next Steps

names() will return the column names of data frames and can be used to change column names as well. rbind() and cbind() combine data frames either by row or by column.

In the next section, we will continue learning how to manipulate data frames.

59.6 Exercises

59.6.1 Question 1

59.6.2 Question 2

59.6.3 Question 3

59.6.4 Question 4

59.6.5 Question 5

59.6.6 Question 6

59.6.7 Question 7

59.6.8 Question 8

59.6.9 Question 9

59.6.10 Question 10