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Introduction
Key elements of the visualization process
Environment - the R Language
20. Summary

## Instruction

You are doing great! Now it's time for a little wrap up of R syntax!

• To assign a value to a variable use the <- operator.
• Put string values in double quotes ("This is a text") or single quotes ('This is also a text').
• There are two logical values in R: TRUE and FALSE. We can use the following logical operators: <, >, <=, >=, !=, & (and), | (or).
• A missing or unknown value is denoted by NA in R.
• Vectors let us store multiple values in one object. To create a vector use the c() function:
family.age <- c(15,19,22,67,65)
• To create a factor, use the factor(vector, levels) function. The first argument gives values, the other specifies levels. If any value from vector is not listed in levels it would be changed to NA.
• A data frame is R's way to store table data.
family <- data.frame(
name = c('Anna','Mark','Tom'),
age = c(30,32,28)
height = c(175, 180, 188)) 
• To access specific elements from a data frame specify their positions in square brackets:
family[c(1,3),c(2,3)]

The first vector is for rows, the second is for columns.
• To narrow a data frame to certain rows, specify the row vector and omit the column vector: family[c(1,2),].
• To narrow a data frame to certain columns, specify the column vector and omit the row vector: family[,c(1,2)].
• To get a whole column from a given data frame use the $ sign with the column name: family$age.