It was an idea for quite some time to write a blog on R, for the benefit of programmers. Basically Sr Managers in the organizations who were programmers or have good coding experience some time in their life.
How can R be used by them easily. The next series of blogs will be on R.
The contents are available in a book form, leave your email in comments and I will mail the book to you. (PDF)
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Chapter 1 Vectors
2.1 Introduction
Unlike in other programming languages in R the following are the
differences.
a. We don’t use
the word variables, rather we use the word vectors. A vector is a data
structure.
b. In other
programming languages for instances we have numbers (int and floats) and arrays
etc. Where as in R everything is an array. So a number is essentially an array with
a single element.
Let us take some examples.
> a<-10 span="">
> b<-c span="">
> a
[1] 10
> b
[1] 10
> class(a)
[1] "numeric"
> class(b)
[1] "numeric"
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Vector a is
defined as a number, where as b is defined as an array. But both are treated
as an array of one number.
The class()
function determines type of the array.
<- a="" and="" assign="" hyphen.="" is="" less="" operator="" span="" than="" the="" to="" value="">
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> a[1]
[1] 10
> b[1]
[1] 10
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As a proof
that both are the same description we can try to print the first element in
the array. Note a also behaves like an array because it is one.
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2.2 Operations in R.
R is rich in operators. Operators can evolve to a numeric value or
to a logical value. Just as I told earlier all variables are essentially
arrays, so a operator works on an array jus like a number.
Look at the following examples.
> a<-10 b="" c="" span="">
> a;b
[1] 10
[1] 10 20 30
> a+10;a*10;a^2;a%%3
[1] 20
[1] 100
[1] 100
[1] 1
> b+10;b*10;b^^2;b%%3
[1] 20 30 40
[1] 100 200 300
> b+10;b*10;b^2;b%%3
[1] 20 30 40
[1] 100 200 300
[1] 100 400 900
[1] 1 2 0
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The ; can be
used to separate multiple commands to be issued in the same row.
The arithmetic
operators +, - * , / are self explanatory. ^ is for the power of.
a^2 here means
a2
%% is the
modulus operator, it gives the remainder.
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> a>10;b>10
[1] FALSE
[1] FALSE
TRUE TRUE
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Logical
operators are supported as well. >, >=, <. <=, !=.
The logical
operators return a logical output.
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2.3 Name in R.
The elements of a vector are accessed by using integers. The first
item is at index 1. R is more interesting in one aspect and that is naming. You
can name a vector’s columns. And then you can use those names for accessing the
items. Look at the following examples to understand more. Remember any line
that begins with a # is treated as a comment.
> sales<-c span="">
> sales
[1] 120 190 90
> sales[1]
[1] 120
> sales[3]
[1] 90
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Here the sales
vector is defined with three numbers. You can check by entering class(sales)
and you get an output NUMERIC.
The elements
are accessed using numbers 1,2… etc.
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> names(sales)<-c an="" ar="" eb="" span="">
> sales
Jan Feb Mar
120 190 90
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The names
function gives names to the columns. Since we have three columns in the sales
vector, we give three names. (Jan, Feb and Mar).
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> max(sales)
[1] 190
>
> sales==max(sales)
Jan Feb
Mar
FALSE TRUE FALSE
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The max is an
inbuilt function that goes thru the vector (sales) and lists the column that
has the max value.
When you list
the sales vector with sales==max(sales), it gives us a logical vector with
TRUE/FALSE values.
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> sales[max.sales]
Feb
190
> class(sales)
[1] "numeric"
> class(max.sales)
[1] "logical"
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Here we create
a new logical vector called max.sales. Remember that vector names can have
. or _ or lower/upper case characters.
The
sales[max.sales] is used to display that column that has the TRUE value.
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That brings an end to chapter 1.
The next page has some exercises for you to try.
2.4 Exercises
1. Download the
R. Goto the following web site to download R.
b. 
c. Create a
folder called c:\R
d. Install R in
this folder.
f. Choose the R
studio desktop free version and install it in the c:\R folder
2. Run the R.exe
from the C:\R\R-3.6.3\bin, if you installed it in c:\R
a. You can do all
the remaining questions from here. If you use R studio then you can do the
exercises from here.
b. 
c. Increase the
size of “Console” window and you can do the exercises from here. If you run
R.exe then the screen looks like this
d. 
e. The back ground
is black and fonts are small by default. Right click on the title bar, goto to
properties
f. 
g. You can set
the colors and fonts from here.
3. Questions that
you need to do.
a. You can run
the sample code that I used during the chapter to test if you see the same
output as the one I have shown.
b. Declare a
numeric vector called train.late with the following (12, 16, 14, 21, 3, 19,9)
c. Give a heading
from Mon to Sun.
d. Assuming that
the numbers are in minutes, find the following
i. On which day
was the train min late
ii. On which day
was the train max late.
iii. What is the
average late in minutes for the train.
iv. On which days
was the train more than 10 minutes late
e. Find the value
of the following equations
i. 32+64
ii. 32+25*4
iii. 32-(25+16)*12
iv. Remainder of
100 divided by 9.
f. Create a
nums.list vector with the following numbers 1,2,3,4
g. Create a
nums.list2 with the following numbers 2,4,6,8
h. Find the
following
i. Nums.list +
nums.list2
ii. Nums.listnums.list2
iii. Nums.list2nums.list
4. You define x<- span="">
a. What is the
output of sort(x)?
b. What if you
want the output in reverse order (max to min)?
