（1） Introduction Guide to R language - the first step of data analysis

notes ： This blog aims to share personal learning experience , Please forgive me for any irregularities ！

R Language

Simply speaking ,R Language is a free open source 、 Powerful programming language for data analysis and visualization .R Please go to R Language website . Download the R After language , It is recommended to download, install and use RStudio This development environment .
When the download is complete , open RStudio, You will see the interface shown in the figure below ：

On the left is Console, You can directly enter the order . If you want to create files and write code , Click the pull-down menu in the top left corner to select . It's commonly used R Script file .

Next, the operation of bloggers can be all in Console in .

Numeric and logical operators

use R It's easy to calculate , Just in Console Type the order in and then enter .
Common numerical operators are shown in the following table ：

Symbol	meaning	give an example
+	Addition operation	5+3 Output is 8
-	Subtraction	7-4 Output is 3
*	Multiplication	2*5 Output is 10
/	Starting operation	10/4 Output is 2.5
^	Index of operation	2^5 Output is 32
%%	model / Take over operations	5%%2 Output is 1
%/%	Division operation	11%/%3 Output is 3

The logical operators commonly used in the following tables ：

Symbol	meaning	explain	give an example
==	be equal to	If the symbols are equal twice , Return to true	4==3 Output is F
>=	Greater than or equal to	If the front of the symbol is greater than or equal to the back of the symbol , Return to true	4>=3 Output is T
<=	Less than or equal to	If the front of the symbol is less than or equal to the back of the symbol , Return to true	4<=3 Output is F
!=	It's not equal to	If the symbols are not equal twice , Return to true	4!=3 Output is T
>	Greater than	If the front of the symbol is greater than the back of the symbol , Return to true	4>3 Output is T
<	Less than	If the front of the symbol is less than the back of the symbol , Return to true	4<3 Output is F
&&	Logic and	If the symbol is true before and after , Return to true	(4==4)&&(3==2) Output is F
||	Logic or	If at least one before or after the symbol is true , Return to true	(4>3)||(4>6) Output is T

Variable type and assignment

R Language variables are generally created without declaring types . In Computational Biology , The following five types of data are the most common ：

type	explain	give an example
character	character string	“abc”
numeric	Floating point numbers Inf Express R The upper limit of NaN Representational image 0/0 Undefined value of	1.02
integer	integer When assigning values, add L, No, the default is numeric	15L
complex	The plural	1+2i
logical	Logical value or Boolean value Case sensitive	T or TRUE F or FALSE

The following commands are used to create variables and assign values to variables / Update value ：

x <- 4
x <- x + 1

After this order is executed , stay Console hit x enter , Will return the current variable x Value (5). stay RStudio On the right side of the Environment I will go out x And its value (5). If you want to know all variables , Please be there. Console Use the following command ：

rm(list= ls())

Complex data structure , Such as vector and data.frame, It will be explained in the subsequent use .

Logical decision and cycle

R Linguistic if else、for、while Grammar and C The language is similar , See the following example for details ：

#if(){}else{}
# If the condition in brackets is true , Then execute the code in curly brackets and end , Otherwise, skip the code in curly brackets 
# Can be in a if Nested in another if, Used to make more complex condition judgments 
# there print() Function can output the contents in parentheses 
# Try at Console Li Da ?print() or ? Add any function you are not sure about and enter , Instructions will appear on the lower right 
x <- 20
y <- 30
if(x<y && y-x>15){
    
	print("Condition 1")
} else {
    
	print("Condition 2")
}
# The output should be "Condition2"

#for(){}
# Determine the number of times the code in curly braces is repeatedly executed according to the range in brackets 
# For example, the following code i in 1:5, You mean for i=1,2,3,4,5
# That is to say, the code will be executed five times 
# Again , Can be in a for loop Nested in another for loop
for(i in 1:5){
    
    print(i^2)
}
# The output should be 1 4 9 16 25

#while(){}
# Loop through the code in curly braces , Until the condition of parentheses is false 
# it is to be noted that , The condition in brackets is always true, and many words will loop 
x <- 1
while(x < 10){
    
    print(x)
    x <- x + 1
}
# The output should be 1 2 3 4 5 6 7 8 9

Conclusion

R That's all for language introduction . I'll explain it in detail next time vector、matrix、list These data structures , Coming soon ！ If you have any questions or suggestions, please leave messages and comments ！