Variable_expressions_statements-R.qmd

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title: "R: Variables, expression and statements"
format:
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    toc: true
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## Data Types

Some of the commonly used objects in R are numbers - integer and double (or numeric), character and logical (TRUE/FALSE). The data type of the object can be identified using the in-built R function `class()` or `typeof()`. For example, see the following objects and their types:


```{r}
class(4)
```

```{r}
typeof(4)
```

```{r}
class(4.4)
```

```{r}
typeof(4.4)
```

```{r}
class(4L)
```

```{r}
typeof(4L)
```


```{r}
class('4')
```

```{r}
typeof('4')
```

```{r}
class(TRUE)
```

```{r}
typeof(FALSE)
```


## Variable names

We have the following rules for a R variable name:

- A variable name must start with a letter and can be a combination of letters, digits, period(.) and underscore(_). If it starts with period(.), it cannot be followed by a digit.
- A variable name cannot start with a number or underscore (_)
- Variable names are case-sensitive (age, Age and AGE are three different variables)
- Reserved words cannot be used as variables (TRUE, FALSE, NULL, if...)

## Converting datatypes

Sometimes a value may have a datatype that is not suitable for using it. For example, consider the variable called `annual_income` in the code below:

```{r}
annual_income = "80000"
```

Suppose we wish to divide `annual_income` by 12 to get the monthly income. We cannot use the variable `annual_income` directly as its datatype is a string and not a number. Thus, numerical operations cannot be performed on the variable `annual_income`.

We’ll need to convert annual_income to an integer. For that we will use the R’s in-built as.integer() function:

```{r}
annual_income = as.integer(annual_income)
monthly_income = annual_income/12
print(paste0("monthly income = ", monthly_income))
```

Similarly, datatypes can be converted from one type to another using in-built R functions as shown below:

```{r}
#Converting integer to character
as.character(9)
```

```{r}
#Converting character to numeric
as.numeric('9.4')
```

```{r}
#Converting logical to integer
as.numeric(FALSE)
```

Sometimes, conversion of a value may not be possible. For example, it is not possible to convert the variable greeting defined below to a number:

```{r}
greeting = "hello"
```

However, strings can be concatenated using the `paste0()` function:

```{r}
paste0("hello", " there!")
```

R’s in-built readline() function can be used to accept an input from the user. For example, suppose we wish the user to input their age:

```{r}
age = readline("Enter your age:")
```

The entered value is stored in the variable `age` and can be used for computation.