Data Frame Creation in R Programming Language: Methods and Examples
Table of Content:
Data frames are used to store tabular data in R. They are an important type of
object in R and are used in a variety of statistical modeling applications. Hadley
Wickham’s package dplyr has an optimized set of functions
designed to work efficiently with data frames.
Data frames are represented as a special type of list where every element of the list has to have the same length. Each element of the list can be thought of as a column and the length of each element of the list is the number of rows.
Unlike matrices, data frames can store different classes of objects in each column. Matrices must have every element be the same class (e.g. all integers or all numeric).
In addition to column names, indicating the names of the variables or predictors, data frames have a special attribute called row.names which indicate information about each row of the data frame.
Data frames are usually created by reading in a dataset using
the read.table() or read.csv(). However, data
frames can also be created explicitly with the data.frame()
function or they can be coerced from other types of objects like lists.
Data frames can be converted to a matrix by calling
data.matrix() . While it might seem that the as.matrix() function
should be used to coerce a data frame to a matrix, almost always, what you want is
the result of data.matrix().
<span class="pln"> </span><span class="pun">></span><span class="pln"> x </span><span class="pun"><-</span><span class="pln"> data</span><span class="pun">.</span><span class="pln">frame</span><span class="pun">(</span><span class="pln">foo </span><span class="pun">=</span><span class="pln"> </span><span class="lit">1</span><span class="pun">:</span><span class="lit">4</span><span class="pun">,</span><span class="pln"> bar </span><span class="pun">=</span><span class="pln"> c</span><span class="pun">(</span><span class="pln">T</span><span class="pun">,</span><span class="pln"> T</span><span class="pun">,</span><span class="pln"> F</span><span class="pun">,</span><span class="pln"> F</span><span class="pun">))</span><span class="pln"> </span><span class="pun">></span><span class="pln"> x foo bar </span><span class="lit">1</span><span class="pln"> </span><span class="lit">1</span><span class="pln"> TRUE </span><span class="lit">2</span><span class="pln"> </span><span class="lit">2</span><span class="pln"> TRUE </span><span class="lit">3</span><span class="pln"> </span><span class="lit">3</span><span class="pln"> FALSE </span><span class="lit">4</span><span class="pln"> </span><span class="lit">4</span><span class="pln"> FALSE </span><span class="pun">></span><span class="pln"> nrow</span><span class="pun">(</span><span class="pln">x</span><span class="pun">)</span><span class="pln"> </span><span class="pun">[</span><span class="lit">1</span><span class="pun">]</span><span class="pln"> </span><span class="lit">4</span><span class="pln"> </span><span class="pun">></span><span class="pln"> ncol</span><span class="pun">(</span><span class="pln">x</span><span class="pun">)</span><span class="pln"> </span><span class="pun">[</span><span class="lit">1</span><span class="pun">]</span><span class="pln"> </span><span class="lit">2</span><span class="pln"> </span>
Names
R objects can havenames, which is very useful for writing readable code and self-describing objects. Here is an example of assigning names to an integer vector.
<span class="pln"> </span><span class="pun">></span><span class="pln"> x </span><span class="pun"><-</span><span class="pln"> </span><span class="lit">1</span><span class="pun">:</span><span class="lit">3</span><span class="pln"> </span><span class="pun">></span><span class="pln"> names</span><span class="pun">(</span><span class="pln">x</span><span class="pun">)</span><span class="pln"> NULL </span><span class="pun">></span><span class="pln"> names</span><span class="pun">(</span><span class="pln">x</span><span class="pun">)</span><span class="pln"> </span><span class="pun"><-</span><span class="pln"> c</span><span class="pun">(</span><span class="str">"New York"</span><span class="pun">,</span><span class="pln"> </span><span class="str">"Seattle"</span><span class="pun">,</span><span class="pln"> </span><span class="str">"Los Angeles"</span><span class="pun">)</span><span class="pln"> </span><span class="pun">></span><span class="pln"> x </span><span class="typ">New</span><span class="pln"> </span><span class="typ">York</span><span class="pln"> </span><span class="typ">Seattle</span><span class="pln"> </span><span class="typ">Los</span><span class="pln"> </span><span class="typ">Angeles</span><span class="pln"> </span><span class="lit">1</span><span class="pln"> </span><span class="lit">2</span><span class="pln"> </span><span class="lit">3</span><span class="pln"> </span><span class="pun">></span><span class="pln"> names</span><span class="pun">(</span><span class="pln">x</span><span class="pun">)</span><span class="pln"> </span><span class="pun">[</span><span class="lit">1</span><span class="pun">]</span><span class="pln"> </span><span class="str">"New York"</span><span class="pln"> </span><span class="str">"Seattle"</span><span class="pln"> </span><span class="str">"Los Angeles"</span><span class="pln"> </span>
Lists can also have names, which is often very useful.
<span class="pln"> </span><span class="pun">></span><span class="pln"> x </span><span class="pun"><-</span><span class="pln"> list</span><span class="pun">(</span><span class="str">"Los Angeles"</span><span class="pln"> </span><span class="pun">=</span><span class="pln"> </span><span class="lit">1</span><span class="pun">,</span><span class="pln"> </span><span class="typ">Boston</span><span class="pln"> </span><span class="pun">=</span><span class="pln"> </span><span class="lit">2</span><span class="pun">,</span><span class="pln"> </span><span class="typ">London</span><span class="pln"> </span><span class="pun">=</span><span class="pln"> </span><span class="lit">3</span><span class="pun">)</span><span class="pln"> </span><span class="pun">></span><span class="pln"> x $</span><span class="str">`Los Angeles`</span><span class="pln"> </span><span class="pun">[</span><span class="lit">1</span><span class="pun">]</span><span class="pln"> </span><span class="lit">1</span><span class="pln"> $Boston </span><span class="pun">[</span><span class="lit">1</span><span class="pun">]</span><span class="pln"> </span><span class="lit">2</span><span class="pln"> $London </span><span class="pun">[</span><span class="lit">1</span><span class="pun">]</span><span class="pln"> </span><span class="lit">3</span><span class="pln"> </span><span class="pun">></span><span class="pln"> names</span><span class="pun">(</span><span class="pln">x</span><span class="pun">)</span><span class="pln"> </span><span class="pun">[</span><span class="lit">1</span><span class="pun">]</span><span class="pln"> </span><span class="str">"Los Angeles"</span><span class="pln"> </span><span class="str">"Boston"</span><span class="pln"> </span><span class="str">"London"</span><span class="pln"> </span>
Matrices can have both column and row names.
<span class="pln"> </span><span class="pun">></span><span class="pln"> m </span><span class="pun"><-</span><span class="pln"> matrix</span><span class="pun">(</span><span class="lit">1</span><span class="pun">:</span><span class="lit">4</span><span class="pun">,</span><span class="pln"> nrow </span><span class="pun">=</span><span class="pln"> </span><span class="lit">2</span><span class="pun">,</span><span class="pln"> ncol </span><span class="pun">=</span><span class="pln"> </span><span class="lit">2</span><span class="pun">)</span><span class="pln"> </span><span class="pun">></span><span class="pln"> dimnames</span><span class="pun">(</span><span class="pln">m</span><span class="pun">)</span><span class="pln"> </span><span class="pun"><-</span><span class="pln"> list</span><span class="pun">(</span><span class="pln">c</span><span class="pun">(</span><span class="str">"a"</span><span class="pun">,</span><span class="pln"> </span><span class="str">"b"</span><span class="pun">),</span><span class="pln"> c</span><span class="pun">(</span><span class="str">"c"</span><span class="pun">,</span><span class="pln"> </span><span class="str">"d"</span><span class="pun">))</span><span class="pln"> </span><span class="pun">></span><span class="pln"> m c d a </span><span class="lit">1</span><span class="pln"> </span><span class="lit">3</span><span class="pln"> b </span><span class="lit">2</span><span class="pln"> </span><span class="lit">4</span><span class="pln"> </span>
Column names and row names can be set separately using the colnames() and rownames()
functions.
<span class="pln"> </span><span class="pun">></span><span class="pln"> colnames</span><span class="pun">(</span><span class="pln">m</span><span class="pun">)</span><span class="pln"> </span><span class="pun"><-</span><span class="pln"> c</span><span class="pun">(</span><span class="str">"h"</span><span class="pun">,</span><span class="pln"> </span><span class="str">"f"</span><span class="pun">)</span><span class="pln"> </span><span class="pun">></span><span class="pln"> rownames</span><span class="pun">(</span><span class="pln">m</span><span class="pun">)</span><span class="pln"> </span><span class="pun"><-</span><span class="pln"> c</span><span class="pun">(</span><span class="str">"x"</span><span class="pun">,</span><span class="pln"> </span><span class="str">"z"</span><span class="pun">)</span><span class="pln"> </span><span class="pun">></span><span class="pln"> m h f x </span><span class="lit">1</span><span class="pln"> </span><span class="lit">3</span><span class="pln"> z </span><span class="lit">2</span><span class="pln"> </span><span class="lit">4</span><span class="pln"> </span>
Note that for data frames, there is a separate function for setting the row names, the row.names() function. Also, data frames do not have column names, they just have names (like lists). So to set the column names of a data frame just use the names() function. Yes, I know its confusing. Here’s a quick summary:
| Object | Set column names | Set row names |
| data frame | names() | row.names() |
| matrix | colnames() | rownames() |
Example of Data Frame
> myvalues1 = c(348, -343, 937, 394, 124) > myvalues2 = c(T, F, T, T, F) > names = c("trial 1", "trial 2", "trial 3", "trial 4", "trial 5") > dataframe1 = data.frame(myvalues1, myvalues2, row.names = names)
Get the Structure of the Data Frame
The structure of the data frame can be seen by using str() function.
> str(dataframe1)
Output
When we execute the above code, it produces the following result ?
'data.frame': 5 obs. of 2 variables: $ myvalues1: num 348 -343 937 394 124 $ myvalues2: logi TRUE FALSE TRUE TRUE FALSE
Summary of Data in Data Frame
The statistical summary and nature of the data can be obtained by applying summary() function.
> # Print the summary. > print(summary(dataframe1))
Output
When we execute the above code, it produces the following result ?
myvalues1 myvalues2 Min. :-343 Mode :logical 1st Qu.: 124 FALSE:2 Median : 348 TRUE :3 Mean : 292 3rd Qu.: 394 Max. : 937
Extract Data from Data Frame
Extract specific column from a data frame using column name.
> # Extract Specific columns. > result <- data.frame(dataframe1$myvalues1) > print(result)
Output
When we execute the above code, it produces the following result ?
dataframe1.myvalues1 1 348 2 -343 3 937 4 394 5 124
Extract the first two rows and then all columns
> # Extract first two rows. > result <- dataframe1[1:2,] > print(result)
Output
When we execute the above code, it produces the following result ?
myvalues1 myvalues2 trial 1 348 TRUE trial 2 -343 FALSE
Extract 3rd and 5th row with 1nd and 2th column
> # Extract 3rd and 5th row with 1nd and 2th column. > result <- dataframe1[c(3,5),c(1,2)] > print(result)
Output
When we execute the above code, it produces the following result ?
myvalues1 myvalues2 trial 3 937 TRUE trial 5 124 FALSE
- Assignment 1: How to Create a data frame in R Programming Language
- Assignment 2: How to set all the column value by a single TRUE value in the data frame
- Assignment 3: How to add a new column in the existing Data frame using R language
- Assignment 4: Add a new column from an existing column with a calculation from the previous column