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# Introduction

Filtering data frames in R is a common task in data analysis. Often we want to subset a data frame to only keep rows that meet certain criteria. A useful filtering technique is keeping rows where a column value falls between two specified values.

In this post, we’ll walk through how to filter rows in R where a column value is between two values using base R syntax.

## Filtering with bracket notation

One way to filter rows is by using bracket notation `[]` and specifying a logical vector.

Let’s create a sample data frame:

```df <- data.frame(
id = 1:10,
value = c(5, 3, 6, 9, 2, 4, 7, 1, 8, 10)
)```

We can filter `df` to only keep rows where `value` is between 5 and 8 with:

`df[df\$value >= 5 & df\$value <= 8,]`
```  id value
1  1     5
3  3     6
7  7     7
9  9     8```

This filters for rows where `value` is greater than or equal to 5 `df\$value >= 5` AND less than or equal to 8 `df\$value <= 8`. The comma after the logical vector tells R to return the filtered rows.

## Filtering with subset()

Another option is using the `subset()` function:

`subset(df, value >= 5 & value <= 8)`
```  id value
1  1     5
3  3     6
7  7     7
9  9     8```

`subset()` takes a data frame as the first argument, then a logical expression similar to the bracket notation.

We can filter on different columns and value ranges:

```# id between 3 and 7
df[df\$id >= 3 & df\$id <= 7,] ```
```  id value
3  3     6
4  4     9
5  5     2
6  6     4
7  7     7```
```# value less than 5
subset(df, value < 5)```
```  id value
2  2     3
5  5     2
6  6     4
8  8     1```

It’s also possible to filter rows outside a range by flipping the logical operators:

```# id NOT between 3 and 7
df[!(df\$id >= 3 & df\$id <= 7),]```
```   id value
1   1     5
2   2     3
8   8     1
9   9     8
10 10    10```
```# value greater than 5
subset(df, value > 5) ```
```   id value
3   3     6
4   4     9
7   7     7
9   9     8
10 10    10```

## Summary

Filtering data frames where a column is between two values is straightforward in R. The key steps are:

• Use bracket notation `df[logical,]` or `subset(df, logical)`
• Create a logical expression with `&` and `>=`, `<=` operators
• Specify the column name and range of values to filter between

I encourage you to try filtering data frames on your own! Subsetting by logical expressions is an important skill for efficient R programming.