How to Use fill() in tidyr to Fill Missing Values in R

Use fill() from the tidyr package to fill missing values in selected columns by carrying the previous or next non-missing value down or up. Specify columns and the direction with .direction argument, like fill(data, column, .direction = "down").

Syntax

The fill() function has this basic syntax:

• data: Your data frame or tibble.
• ... (columns): One or more columns to fill missing values in.
• .direction: Direction to fill missing values, either "down" (default), "up", "downup", or "updown".

r

fill(data, ..., .direction = "down")

Example

This example shows how to fill missing values in a column by carrying the last observed value downwards.

r

library(tidyr)
library(dplyr)

data <- tibble(
  group = c("A", NA, NA, "B", NA, "C", NA),
  value = c(1, NA, 3, NA, 5, NA, 7)
)

filled_data <- data %>%
  fill(group, .direction = "down")

print(filled_data)

Output

# A tibble: 7 × 2
  group value
  <chr> <dbl>
1 A         1
2 A        NA
3 A         3
4 B        NA
5 B         5
6 C        NA
7 C         7

Common Pitfalls

Common mistakes when using fill() include:

• Not specifying columns, which fills all columns and may cause unexpected changes.
• Using the wrong .direction, leading to filling in the wrong direction.
• Expecting fill() to fill non-missing gaps that require interpolation (it only copies existing values).

r

library(tidyr)

# Wrong: fills all columns unintentionally
filled_wrong <- fill(tibble(x = c(1, NA), y = c(NA, 2)))

# Right: specify columns to fill
filled_right <- fill(tibble(x = c(1, NA), y = c(NA, 2)), x)

print(filled_wrong)
print(filled_right)

Output

# A tibble: 2 × 2
      x     y
  <dbl> <dbl>
1     1    NA
2     1     2

# A tibble: 2 × 2
      x     y
  <dbl> <dbl>
1     1    NA
2     1     2

Quick Reference

Argument	Description
data	Data frame or tibble to fill missing values in
...	Columns to fill (unquoted names)
.direction	Direction to fill: "down" (default), "up", "downup", or "updown"

Key Takeaways

Use fill() to replace missing values by copying nearby non-missing values in specified columns.

Specify columns explicitly to avoid filling unintended columns.

Choose the correct .direction to control whether values fill downward, upward, or both.

fill() copies existing values; it does not interpolate or calculate new values.

fill() is useful for cleaning data with missing entries in grouped or ordered datasets.