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Creating a frequency table of multiple variables in R can be done by using the table() function. This function takes multiple parameters in the form of vectors and returns a multi-dimensional array of the frequency distribution for each of the variables. It is also possible to pass additional arguments to the table() function such as row/column headings and other options in order to customize the table to your needs.
To calculate a frequency table for multiple variables in a data frame in R you can use the apply() function, which uses the following syntax:
apply(X, MARGIN FUN)
where:
- X: An array, matrix, or data frame
- MARGIN: Apply a function across rows (1) or columns (2)
- FUN: The function to be applied
The following examples show how to use this syntax in practice.
Example 1: Frequency Table for All Variables in R
The following code shows how to calculate a frequency table for every variable in a data frame:
#create data frame df <- data.frame(var1=c(1, 1, 2, 2, 2, 2, 3), var2=c('A', 'A', 'A', 'A', 'B', 'B', 'B'), var3=c(6, 7, 7, 7, 8, 8, 9)) #view first few rows of data frame head(df) var1 var2 var3 1 1 A 6 2 1 A 7 3 2 A 7 4 2 A 7 5 2 B 8 6 2 B 8 #calculate frequency table for every variable in data frame apply((df), 2, table) $var1 1 2 3 2 4 1 $var2 A B 4 3 $var3 6 7 8 9 1 3 2 1
The result is three frequency tables – one for each variable in the data frame.
Here’s how to interpret the first frequency table:
- The value 1 appears 2 times in the “var1” column
- The value 2 appears 4 times in the “var2” column
- The value 3 appears 1 time in the “var3” column
The other frequency tables can be interpreted in a similar manner.
Example 2: Frequency Table for Specific Variables in R
The following code shows how to calculate a frequency table for specific variables in a data frame
#create data frame df <- data.frame(var1=c(1, 1, 2, 2, 2, 2, 3), var2=c('A', 'A', 'A', 'A', 'B', 'B', 'B'), var3=c(6, 7, 7, 7, 8, 8, 9)) #calculate frequency table for var1 and var3 columns apply((df[c('var1', 'var3')]), 2, table) $var1 1 2 3 2 4 1 $var3 6 7 8 9 1 3 2 1
Example 3: Frequency Table for All But One Variable in R
Suppose we have an index column in a data frame and we would like to calculate a frequency table for every variable in the data frame except the index column.
#create data frame df <- data.frame(index=c(1, 2, 3, 4, 5, 6, 7), var2=c('A', 'A', 'A', 'A', 'B', 'B', 'B'), var3=c(6, 7, 7, 7, 8, 8, 9)) #calculate frequency table for all columns except index column apply((df[-1]), 2, table) $var2 A B 4 3 $var3 6 7 8 9 1 3 2 1