csv_io

csv_io, R programs which illustrate how one can read or write comma separated value (CSV) files.

Briefly, R includes a special command read.csv() specifically for reading CSV files:

        name <- read.csv ( "filename.csv",
          header = TRUE or FALSE )

or, the more general read.table() function can be used:

        name <- read.table ( "filename.csv",
          header = TRUE or FALSE,
          sep = "," or sep = " " or sep= "\t" )

The simplest example of a comma separated value file involves numeric data, with the same number of values occurring on each row. Thus, we might have three rows of data, each containing 10 values, with successive values separated by commas (which R specifies by sep=","):

1,2,3,4,5,6,7,8,9,10
11,12,13,14,15,16,17,18,19,20
21,22,23,24,25,26.27.28.29,30

Variations on this approach use the TAB character (which R specifies by sep="\t") to separate the values:

1	2	3	4	5	6	7	8	9	10
11	12	13	14	15	16	17	18	19	20
21	22	23	24	25	26	27	28	29	30

or one or more spaces (which R specifies by sep=" ":

 1  2  3  4  5  6  7  8  9 10
11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30

Sometimes the first row of a CSV file is used to give labels to the columns. In this case, the command to read the file should specify header=TRUE:

        "Age", "Weight in Pounds"
        0,  8.4
        1, 16.8
        2, 24.5
        3, 37.0
        4, 49.0
        5, 63.0

A data frame is a table of data that may include row or column labels as well. For instance, the FAMILY example defines a data frame of 4 properties of 7 individuals, which can be represented as the following table, where items in bold face are labels:

First name Age Height (inches) Weight (pounds)

Dad Horace 45 71 230

Mom Gladys 43 66 158

Big Bro Marco 22 73 190

Big Sis Desiree 20 69 150

Me Arnold 17 69 165

Punk Sis Darleen 15 67 120

Dog Blotch 3 12 15

If this data frame is written to a CSV file, the first row of the file contains column labels, and the subsequent rows each begin with the row label followed by the data for that row.

	First name	Age	Height (inches)	Weight (pounds)
Dad	Horace	45	71	230
Mom	Gladys	43	66	158
Big Bro	Marco	22	73	190
Big Sis	Desiree	20	69	150
Me	Arnold	17	69	165
Punk Sis	Darleen	15	67	120
Dog	Blotch	3	12	15

Licensing:

The computer code and data files on this web page are distributed under the MIT license

Languages:

csv_io is available in a FORTRAN90 version and an R version.

Related Data and Programs:

XLS_IO R programs which illustrate how data can be shared between Microsoft EXCEL and R, using XLS and CSV files.

Reference:

Joseph Adler,
R in a Nutshell,
O'Reilly, 2009,
ISBN13: 978-0-596-80170-0.
http://www.r-project.org, the official R web site.
http://cran.r-project.org/doc/manuals/R-data.pdf, R Data Import/Export

Examples and Tests:

PLAYERS is an example involving the highest salaried football players. The data includes first and last name, team, position, and salary, for 5 players. The file includes an initial row of column labels. The data is separated by commas.

create_players.R, defines the data and assigns it to a data frame.
write_players.R, writes the data frame to the file "players.csv".
read_players.R, reads the data frame from the file "players.csv".
players.sh, runs all the tests.
players.txt, the output file.

players.csv, the comma separated value file containing the player information.

NUMBERS is an example in which no column or row labels are used, and all the data is numeric, consisting of 3 rows of 10 numbers. The basic file uses commas to separate the data, but two related files use tabs or spaces instead.

read_numbers.R, reads and prints the data from all three files.
read_numbers.sh, runs all the tests.
read_numbers.txt, the output file.

numbers.csv, the comma separated value file containing the numbers.
numbers_tab.csv, the tab separated value file containing the numbers.
numbers_space.csv, the space separated value file containing the numbers.

FAMILY is an example in which column and row labels are used. In fact, the default labels used by R are replaced by user-chosen values. The values and labels are written to the CSV file, and read back.

create_family.R, defines the data, assigns it to a data frame, and replaces the default row and column labels by user-chosen values.
write_family.R, writes the data frame to the file "family.csv".
read_family.R, reads the data frame from the file "family.csv".
family.sh, runs all the tests.
family.txt, the output file.

family.csv, the comma separated value file containing the data, as well as row and column labels.

Last modified on 27 May 2020.