**Data Types**

Unlike SAS and SPSS, R has several different data types (structures) including vectors, factors, data frames, matrices, arrays, and lists. The data frame is most like a dataset in SAS.

**1. Vectors**

A vector is an object that contains a set of values called its elements.

**Numeric vector**

x <- c(1,2,3,4,5,6)

*The operator <– is equivalent to "=" sign.*

**Character vector**

State <- c("DL", "MU", "NY", "DL", "NY", "MU")

*To calculate frequency for State vector, you can use*

**table**function.

*To calculate mean for a vector, you can use*

**mean**function.*Since the above vector contains a NA (not available) value, the mean function returns NA.*

*To calculate mean for a vector*

**excluding NA values**, you can include

**na.rm = TRUE**parameter in mean*function.*

**Convert a column "x" to numeric**

data$x = as.numeric(data$x)

**2.**

**Factors**

R has a special data structure to store

**. It tells R that a variable is nominal or ordinal by making it a factor.**

*categorical variables*The factor function has three parameters:

- Vector Name
- Values (Optional)
- Value labels (Optional)

**Convert a column "x" to factor**

data$x = as.factor(data$x)

**3.**

**Matrices**

All values in columns in a matrix must have the same mode (numeric, character, etc.) and the same length.

The

**cbind**function joins columns together into a matrix. See the usage below

The numbers to the left side in brackets are the row numbers. The form [1, ] means that it is row number one and the blank following the comma means that R has displayed all the columns.

To see dimension of the matrix, you can use

**dim**function.

To see correlation of the matrix, you can use

**cor**function.

You can use subscripts to identify rows or columns.

**4. Arrays**

Arrays are similar to matrices but can have more than two dimensions.

**5. Data Frames**

A data frame is similar to SAS and SPSS datasets. It contains variables and records.

It is more general than a matrix, in that different columns can have different modes (numeric, character, factor, etc.

The

**data.frame**function is used to combine variables (vectors and factors) into a data frame.

**6. Lists**

A list allows you to store a variety of objects.

You can use subscripts to select the specific component of the list.

**How to know data type of a column**

1.

**'class'**is a property assigned to an object that determines how generic functions operate with it. It is not a mutually exclusive classification.

2.

**'mode'**is a mutually exclusive classification of objects according to their basic structure. The 'atomic' modes are numeric, complex, charcter and logical.

> x <- 1:16

> x <- factor(x)

> class(x)

[1] "factor"

> mode(x)

[1] "numeric"

Congrats, Mr. Bhalla. This post was very clear, straight and useful. Thanks for sharing it with us.

ReplyDeleteThank you for your appreciation. Glad you found it useful.

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ReplyDeletegreat, easy to understand for user who is starting yet!

ReplyDeleteI have knowledge of R and looking for visulization of data sets, if have any specific link, request to you, please share it to me.

what is the correlation? can you please explain that part

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ReplyDeleteSuch great content..

ReplyDeleteCould you please specify what's the difference between List and Array then?

Does an array cannot contain any of the things such as 'vectors', 'factors', etc?

Can vector be 2-dimensional?

Thanks!

Thanks a lot for this great R tutorial!

ReplyDelete