# Assignment, Types and Basic Operations — R Programming

Source: https://www.geekswithgeeks.com/en/r-programming/f-basics

> Assign values and use R's atomic types, special values and type checks.

## The building blocks

Assign values with **`<-`** (the conventional R assignment operator; `=` also works at the top level, and RStudio inserts `<-` with Alt and minus). Names are case-sensitive and conventionally use `snake_case`. R's basic **atomic types** are **double** (numbers, the default: `3` is a double), **integer** (written with `L`: `3L`), **character** (strings in double or single quotes), **logical** (`TRUE`/`FALSE`), **complex** and raw. Even a single value is a **vector of length one**. Check types with `typeof()`, `class()` and functions such as `is.numeric()`, and convert with `as.numeric()`, `as.character()` and `as.integer()` (failed conversions produce `NA` with a warning). Special values: **`NA`** (missing value, which propagates: `NA + 1` is `NA`), **`NULL`** (absence of a value), `NaN` (not a number) and `Inf`. Arithmetic includes `%/%` (integer division) and `%%` (remainder). Use `paste()`/`paste0()` or `sprintf()` to build strings, and `print()`, `cat()` or simply typing a name in the console to see values.

## Types, conversions and missing values

NA propagates through calculations unless you remove it explicitly.

```r
price <- 499.5                 # double
qty <- 3L                      # integer
city <- "Pune"                 # character
in_stock <- TRUE               # logical

typeof(qty)                    # "integer"
class(price)                   # "numeric"

total <- price * qty
paste0("Total for ", qty, " items in ", city, ": ", total)
sprintf("%.2f INR", total)

as.numeric("42")               # 42
as.numeric("forty-two")        # NA with a warning

marks <- c(72, NA, 90)
mean(marks)                    # NA: missing values propagate
mean(marks, na.rm = TRUE)      # 81: ignore missing values

17 %/% 5                       # 3 (integer division)
17 %% 5                        # 2 (remainder)
```

## NA is contagious

Any calculation involving NA returns NA, and `x == NA` is always NA, never TRUE. Use `is.na(x)` to test for missing values and `na.rm = TRUE` in summary functions.

**Quiz:** What does mean(c(72, NA, 90)) return?

- [ ] 81
- [ ] 0
- [x] NA
- [ ] An error

*Answer:* NA. Missing values propagate unless na.rm = TRUE is used.