R Data Structures
There are 4 basic data structures in R. I am not referring to the basic data types (numeric, integer, character, logical, complex ).
1. Vector – Sequence of elements of the same basic data type.
# These are some examples of vectors. # A numeric vector showing temperatures in Chicago of a particular week. > temp = c(12.4, 13.5, 15.6, 20, 21.5, 13.6, 12.4) > temp [1] 12.4 13.5 15.6 20.0 21.5 13.6 12.4
# You cannot have different data types in a vector. # Since 12.4 is now defined as a string, all of the numbers have been # converted to strings automatically. > temp = c(12.4, 13.5, 15.6, 20, 21.5, 13.6, "12.4") > temp [1] "12.4" "13.5" "15.6" "20" "21.5" "13.6" "12.4"
2. Matrix – If a Vector is 1D (1-dimensional), a matrix is 2D
# For example, if the vector temp_month contains the temperatures in # Chicago for an entire month > temp_month [1] 12.4 13.5 15.6 20.0 21.5 13.6 12.4 13.2 12.6 17.6 [11] 12.8 19.4 14.3 16.7 17.2 14.5 16.7 19.2 21.5 14.0 [21] 19.4 19.3 17.5 18.5 20.1 22.5 23.5 34.1
<pre class="wp-block-syntaxhighlighter-code"># this can be folded into a 4x7 matrix as below > month_matrix = matrix(temp_month, nrow=4, ncol=7, byrow=TRUE)<div>> month_matrix</div><div> [,1] [,2] [,3] [,4] [,5] [,6] [,7] [1,] 12.4 13.5 15.6 20.0 21.5 13.6 12.4 [2,] 13.2 12.6 17.6 12.8 19.4 14.3 16.7 [3,] 17.2 14.5 16.7 19.2 21.5 14.0 19.4 [4,] 19.3 17.5 18.5 20.1 22.5 23.5 34.1</div></pre>
3. List – Like a vector, but not limited to “same data type”
# For example, different data types like a person's age (numeric), # name(string), city(string),zip code (numeric) can be stored in a list. > person = list(30, "Ajay", "San Francisco", 94000 ) > person [[1]] [1] 30 [[2]] [1] "Ajay" [[3]] [1] "San Francisco" [[4]] [1] 94000
4. Data Frame – Like a Matrix, but not limited to “same data type”
<pre class="wp-block-syntaxhighlighter-code"># A data frame is usually created by reading from external data
# using functions like read.csv() or read.table().
# Imagine 4 vectors
> age = c(30,32,21,60)<div>> names = c("Ajay","Adam","Mary","Aishu")
> cities = c("San Francisco","New York","Sunnyvale","San Jose")
> zip = c(94000,40101,94010,94001)
</pre>
<pre class="wp-block-syntaxhighlighter-code"># We can combine the vectors into a data frame like so > persons = data.frame(age,names,cities,zip)<div>> persons</div><div> age names cities zip 1 30 Ajay San Francisco 94000 2 32 Adam New York 40100 3 21 Mary Sunnyvale 94010 4 60 Aishu San Jose 94001</div></div> </pre>