UC Business Analytics R Programming Guide

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Adding on to Data Frames

We can leverage the cbind() function for adding columns to a data frame. Note that one of the objects being combined must already be a data frame otherwise cbind() could produce a matrix.

df
##   col1 col2  col3     col4
## 1    1 this  TRUE 2.500000
## 2    2   is FALSE 4.200000
## 3    3 text  TRUE 3.141593

# add a new column
v4 <- c("A", "B", "C")

cbind(df, v4)
##   col1 col2  col3     col4 v4
## 1    1 this  TRUE 2.500000  A
## 2    2   is FALSE 4.200000  B
## 3    3 text  TRUE 3.141593  C

We can also use the rbind() function to add data frame rows together. However, severe caution should be taken because this can cause changes in the classes of the columns. For instance, our data frame df currently consists of an integer, character, logical, and numeric variables.

df
##   col1 col2  col3     col4
## 1    1 this  TRUE 2.500000
## 2    2   is FALSE 4.200000
## 3    3 text  TRUE 3.141593

str(df)
## 'data.frame':	3 obs. of  4 variables:
##  $ col1: int  1 2 3
##  $ col2: chr  "this" "is" "text"
##  $ col3: logi  TRUE FALSE TRUE
##  $ col4: num  2.5 4.2 3.14

If we attempt to add a row using rbind() and c() it converts all columns to a character class. This is because all elements in the vector created by c() must be of the same class so they are all coerced to the character class which coerces all the variables in the data frame to the character class.

df2 <- rbind(df, c(4, "R", F, 1.1))

df2
##   col1 col2  col3             col4
## 1    1 this  TRUE              2.5
## 2    2   is FALSE              4.2
## 3    3 text  TRUE 3.14159265358979
## 4    4    R FALSE              1.1

str(df2)
## 'data.frame':	4 obs. of  4 variables:
##  $ col1: chr  "1" "2" "3" "4"
##  $ col2: chr  "this" "is" "text" "R"
##  $ col3: chr  "TRUE" "FALSE" "TRUE" "FALSE"
##  $ col4: chr  "2.5" "4.2" "3.14159265358979" "1.1"

To add rows appropriately, we need to convert the items being added to a data frame and make sure the columns are the same class as the original data frame.

adding_df <- data.frame(col1 = 4, col2 = "R", col3 = FALSE, col4 = 1.1, 
                 stringsAsFactors = FALSE)

df3 <- rbind(df, adding_df)

df3
##   col1 col2  col3     col4
## 1    1 this  TRUE 2.500000
## 2    2   is FALSE 4.200000
## 3    3 text  TRUE 3.141593
## 4    4    R FALSE 1.100000

str(df3)
## 'data.frame':	4 obs. of  4 variables:
##  $ col1: num  1 2 3 4
##  $ col2: chr  "this" "is" "text" "R"
##  $ col3: logi  TRUE FALSE TRUE FALSE
##  $ col4: num  2.5 4.2 3.14 1.1

There are better ways to join data frames together than to use cbind() and rbind(). These are covered later on in the transforming your data with dplyr tutorial.