6.1. Basic Data Manipulation

6.1.1. Editing

Two functions are available for basic editing of data: edit and fix. They work on objects like vectors, matrices, data frames, etc.. Both of them open an editor for the user to make changes in the data object. After the editing is done, fix changes the object in place while edit returns a new object.

For updating an object using edit function:

> obj <- edit(obj)

This is same as

> fix(obj)

The result of edit operation can be assigned to a new object too:

> obj2 <- edit(obj)

6.1.2. Loading and Saving R Objects

Saving an R object:

save(obj, file='<filename>.rda')

Loading an R object:

load('<filename>.rda')

6.1.3. Reading and Writing Matrices and Vectors

Put this data into a file named simple_3x4_matrix.txt:

0 1 2 3
4 5 6 7
8 9 10 11

Reading the numbers as a vector

> scan('simple_3x4_matrix.txt')
Read 12 items
 [1]  0  1  2  3  4  5  6  7  8  9 10 11

Reading as a matrix via scan:

> matrix(scan('simple_3x4_matrix.txt'), nrow=3)
Read 12 items
     [,1] [,2] [,3] [,4]
[1,]    0    3    6    9
[2,]    1    4    7   10
[3,]    2    5    8   11
> matrix(scan('simple_3x4_matrix.txt'), nrow=3, byrow = T)
Read 12 items
     [,1] [,2] [,3] [,4]
[1,]    0    1    2    3
[2,]    4    5    6    7
[3,]    8    9   10   11

6.1.4. Reading and Writing Tables

Writing a data frame to file:

> d = data.frame(a=rnorm(3), b=rnorm(3))
> d
           a          b
1  0.9914006 -0.4930738
2 -0.5068710  0.5471745
3 -1.9964106  0.2247440
> write.table(d, file="tst0.txt", row.names=FALSE)

Reading a data frame from file:

> d2 = read.table(file="tst0.txt", header=TRUE)

Reading a table and converting it to a matrix:

> read.table('simple_3x4_matrix.txt')
  V1 V2 V3 V4
1  0  1  2  3
2  4  5  6  7
3  8  9 10 11
> as.matrix(read.table('simple_3x4_matrix.txt'))
     V1 V2 V3 V4
[1,]  0  1  2  3
[2,]  4  5  6  7
[3,]  8  9 10 11

Functions for reading tabular data and their defaults

Function	Purpose	Header	Separator	Decimal
read.table	Read tabular data from file	Absent		.
read.csv	Read from comma separated value files	Present	,	.
read.csv2	Read from semicolon separated value files	Present	;	,
read.delim	Read from tab delimited files	Present	\t	.
read.delim2	Read from tab delimited files	Present	\t	,

Suggestions

• Use nrows= argument to read only a few rows first to ensure that all the options to the reading function have been provided correctly.

Reading a table from a text string

Let the tabular data be stored in a character string text:

> my.data <- '
+ x y z
+ 1 2 3
+ 2 2 3
+ 3 2 4
+ 4 2 1
+ '

Let’s prepare a connection to the text string:

> con <- textConnection(my.data)

Let us read the table from the text connection:

> read.table(con, header=T)
  x y z
1 1 2 3
2 2 2 3
3 3 2 4
4 4 2 1