Perhaps you want to get the first few letters of a product code or the area code from a phone number. In this blog post, we'll explore how to extract the first three characters from a column in an R dataframe.

## The Problem

Let's say we have a dataframe with a column containing strings, and we want to create a new column with just the first three characters of each string. How can we do this efficiently in R?

## The Solution: substr()

R provides a handy function called `substr()` that allows us to extract a substring from a string. Here's how we can use it to solve our problem:

```R
# Create a sample dataframe
df <- data.frame(
  id = 1:5,
  product_code = c("ABC123", "DEF456", "GHI789", "JKL012", "MNO345")
)

# Extract the first three characters
df$short_code <- substr(df$product_code, start = 1, stop = 3)

# View the result
print(df)
```

Let's break down what's happening here:

1. We create a sample dataframe `df` with an `id` column and a `product_code` column.
2. We use `substr()` to extract characters from `product_code`:
   - The first argument is the string we're extracting from (`df$product_code`).
   - `start = 1` tells it to begin at the first character.
   - `stop = 3` tells it to stop at the third character.
3. We assign the result to a new column `short_code`.

The output will look like this:

```
  id product_code short_code
1  1       ABC123        ABC
2  2       DEF456        DEF
3  3       GHI789        GHI
4  4       JKL012        JKL
5  5       MNO345        MNO
```

## Using stringr for More Complex Operations

If you find yourself doing a lot of string manipulation, you might want to check out the `stringr` package. It provides a consistent, easy-to-use set of functions for working with strings. Here's how you could solve the same problem using `stringr`:

```R
library(stringr)

df$short_code <- str_sub(df$product_code, start = 1, end = 3)
```

This does the same thing as our `substr()` example, but `stringr` functions can be easier to remember and use, especially for more complex string operations.

## Conclusion

Extracting substrings from your dataframe columns is a common task in data cleaning and feature engineering. Whether you use base R's `substr()` or `stringr`'s `str_sub()`, you now have the tools to easily extract the first three (or any number of) characters from your dataframe columns.

Remember, these functions are versatile - you can extract any continuous subset of characters by adjusting the `start` and `stop`/`end` parameters. Happy coding!

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