# Count Number of Rows in R

Manav Narula Jan 30, 2023 Dec 30, 2020

In real-life examples, we encounter large datasets containing hundreds and thousands of rows and columns. To work on such large chunks of data, we need to be familiar with the rows, columns, and data types.

This tutorial will introduce how to count the number of rows by group in R.

## Use the `data.frame(table())` Function to Count Number of Rows in R

The `data.frame(table())` function creates a table with the count of different factor values. It counts the total unique rows of a column. We can easily pass the required column of the DataFrame to the function. See the following code snippet.

``````df <- data.frame(Name = c("Jack","Jay","Mark","Sam"),
Month = c("Jan","Jan","May","July"),
Age = c(12,10,15,13))
data.frame(table(df\$Month))
``````

Output:

`````` Var1 Freq
1  Jan    2
2 July    1
3  May    1
``````

## Use the `count()` Function to Count Number of Rows in R

The `plyr` library in R performs basic data manipulation tasks like splitting data, performing some function, and merging it afterward. It has a function `count()` which returns the frequency of unique rows of a DataFrame. We have to pass the DataFrame and column name as its parameter, as shown below:

``````df <- data.frame(Name = c("Jack","Jay","Mark","Sam"),
Month = c("Jan","Jan","May","July"),
Age = c(12,10,15,13))
library(plyr)
count(df, "Month")
``````

Output:

``````  Month freq
1   Jan    2
2  July    1
3   May    1
``````

## Use the `ddply()` Function to Count Number of Rows in R

Another interesting function provided in the `plyr` library is the `ddply()` function. It splits the data into a subset, specifies some function to be applied to the data, and combine the result. In the example below, we will pass the DataFrame and column name to the function and the `nrow` function as parameters:

``````df <- data.frame(Name = c("Jack","Jay","Mark","Sam"),
Month = c("Jan","Jan","May","July"),
Age = c(12,10,15,13))
library(plyr)
ddply(df, .(Month), nrow)
``````

Output:

``````  Month V1
1   Jan  2
2  July  1
3   May  1
``````
Author: Manav Narula

Manav is a IT Professional who has a lot of experience as a core developer in many live projects. He is an avid learner who enjoys learning new things and sharing his findings whenever possible.