In this tutorial, we will show you what the spread() function in R is and how to use it. The spread() function is often used to reformat a data frame from long format to short format. Check out the instructions below for more details.
Spread() function in R
What does the spread() function do in R?
Let’s take a look at this example:
We have this dataset:
Group Vehicles Amount
1 Group 1 car 1
2 Group 2 bike 3
3 Group 3 bike 2
4 Group 2 car 2
5 Group 1 bike 4
6 Group 3 car 3We want to count each type of vehicle in each group. However, the current table is quite hard to do that. So instead, we will take each type of vehicles as new columns like this:
Group bike car
1 Group 1 4 1
2 Group 2 3 2
3 Group 3 2 3And we do this by using the spread() function. The spread() function will spread a key-value pair across multiple columns, or we can say that it reshapes our data frame from long to short.
Syntax:
spread(df, key, value)
Parameters:
- df: the data frame which we want to change.
- key: the columns in which its values are the new columns’ names.
- value: the columns in which its values will be used to fill in the new columns created by the new keys. Or, in short, the values of the new keys.
How to use spread() in R
Let’s say we have this data frame that represents the number of 3 different kinds of fruits that each class as a school needs for their students.
dataFrame <- data.frame(
class = c("Class A", "Class B", "Class C", "Class D",
"Class B", "Class A", "Class D", "Class C",
"Class D", "Class A", "Class B", "Class C"),
fruit = c("apple", "orange", "apple", "pea", "pea", "orange",
"apple", "pea", "orange", "pea", "apple", "orange"),
quantity = c(15, 23, 19, 17, 21, 20, 21, 14, 24, 19, 18, 20)
)
dataFrameOur data frame:
class fruit quantity
1 Class A apple 15
2 Class B orange 23
3 Class C apple 19
4 Class D pea 17
5 Class B pea 21
6 Class A orange 20
7 Class D apple 21
8 Class C pea 14
9 Class D orange 24
10 Class A pea 19
11 Class B apple 18
12 Class C orange 20However, this table is not really suitable for this kind of data and thus hard to follow. Instead, we will use the spread() function to make key-value columns become a set of columns.
To use the spread() function in R, first, we have to install the ‘tidyr‘ library.
Type in the console:
install.packages("tidyr")Then load the library using:
library(tidyr)Now we can use the spread() function in our program. In our data frame, we will want the key to be the 3 types of fruit and the value is the quantity, so key=fruit and value=quantity.
spread(dataFrame, key = fruit, value = quantity)
Completed code:
dataFrame <- data.frame(
class = c("Class A", "Class B", "Class C", "Class D",
"Class B", "Class A", "Class D", "Class C",
"Class D", "Class A", "Class B", "Class C"),
fruit = c("apple", "orange", "apple", "pea", "pea", "orange",
"apple", "pea", "orange", "pea", "apple", "orange"),
quantity = c(15, 23, 19, 17, 21, 20, 21, 14, 24, 19, 18, 20)
)
library(tidyr)
spread(dataFrame, key = fruit, value = quantity)Output:
class apple orange pea
1 Class A 15 20 19
2 Class B 18 23 21
3 Class C 19 20 14
4 Class D 21 24 17As you can see, this new table is much more readable and easy to count how many of each kind of fruits each class needs.
Summary
In this tutorial, we have shown you the definition of the spread() function in R and its applications. This is a really useful function if you want to use the values of a column to create other columns and make the data frame shorter and wider.
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Hello. My name is Khanh Hai Ngo. I graduated in Information Technology at VinUni. My advanced programming languages include C, C++, Python, Java, JavaScript, TypeScript, and R, which I would like to share with you. You will benefit from my content.
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Programming Languages: C, C++, Python, Java, JavaScript, TypeScript, R