summarize in r, when we have a dataset and need to get a clear idea about each parameter then a summary of the data is important. Summarized data will provide a clear idea about the data set.

In this tutorial we are going to talk about summarize () function from dplyr package. Summarizing a data set by group gives better indication on the distribution of the data.

This tutorial you will get the idea about summarise(), group_by summary and important functions in summarise()

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Load Library

library(dplyr)

Let’s load iris data set for summarization. Let’s store the iris data set into new variable say df for summarize in r.

df<-iris
df1<-summarise(df, mean(Sepal.Length())

Output:-

mean(Sepal.Length)
5.843333

Let’s create mean and sd of Sepal Length.

df2<-summarise(df, Mean=mean(Sepal.Length(),
SD=sd(Sepal.Length())

Output:-

   Mean       SD
5.843333 0.8280661

Now we try to summarize based on groups.

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df3<-summarise(group_by(df, Species),
Mean=mean(Sepal.Length(),
SD=sd(Sepal.Length())

Output:-

   Species     Mean    SD          
 1 setosa      5.01 0.352
 2 versicolor  5.94 0.516
 3 virginica   6.59 0.636

You can make use of pipe operator for summarising the data set.

Pipe operator comes under magrittr package. Let’s load the package.

library(magrittr)
df4<-df %>%
  group_by(Species) %>%
  summarise(Mean = mean(Sepal.Length),
            SD=sd(Sepal.Length))

Output:-

   Species     Mean    SD          
 1 setosa      5.01 0.352
 2 versicolor  5.94 0.516
 3 virginica   6.59 0.636

Based on pipe operator you can easily summarize and plot it with the help of ggplot2.

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library(ggplot2)

For plotting the datset we have main four steps

Step 1: Select the appropriate data frame

Step 2: Group the data frame

Step 3: Summarize the data frame

Step 4: Plot the summary statistics based on your requirement

df %>%
  group_by(Species) %>%
  summarise(Mean = mean(Sepal.Length)) %>%
  ggplot(aes(x = Species, y = Mean, fill = Species)) +
  geom_bar(stat = "identity") +
  theme_classic() +
  labs(
    x = "Species",
    y = "Average Sepal.Length ",
    title = paste(
      "Summary Based on Groups"
    )
  )

Sum

Another useful function to aggregate the variable is sum().

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df5<-df %>%
  group_by(Species) %>%
  summarise(sum = sum(Sepal.Length),
            SD=sd(Sepal.Length))

Output:-

   Species      sum    SD          
 1 setosa      250  0.352
 2 versicolor  297  0.516
 3 virginica   329  0.636

Minimum and maximum

Find the minimum and the maximum of a vector or variable with the help of function min() and max().

df6<-df %>%
  group_by(Species) %>%
  summarise(Min = min(Sepal.Length),
            Max=max(Sepal.Length))

Output:-

  Species      Min   Max          
 1 setosa       4.3   5.8
 2 versicolor   4.9   7  
 3 virginica    4.9   7.9

Count

Suppose if you want to count observations by group you can aggregate the number of occurrence with n().

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df7<-df %>%
  group_by(Species) %>%
  summarise(Sepal.Length = n())%>%
            arrange(desc(Sepal.Length))

Output:-

   Species    Sepal.Length                
 1 setosa               50
 2 versicolor           50
 3 virginica            50

First and Last

Some cases first cases or position identification is important, then you can make use of first, last or nth position of a group.

df8<-df %>%
  group_by(Species) %>%
  summarise(First = first(Sepal.Length),
            Last=last(Sepal.Length))

Output:-

   Species    First  Last          
 1 setosa       5.1   5  
 2 versicolor   7     5.7
 3 virginica    6.3   5.9

The same way you can make use of following functions some of the functions already covered in the tutorial.

You can see the important functions below for summarizing the dataset.

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Mean

summarise(df,mean = mean(x1))

Median

summarise(df,median = median(x1))

Sum

summarise(df,sum = sum(x1))

Standard Deviation

summarise(df,sd = sd(x1))

Interquartile

summarise(df,interquartile = IQR(x1))

Minimum

summarise(df,minimum = min(x1))

Maximum

summarise(df,maximum = max(x1))

Quantile

summarise(df,quantile = quantile(x1))

First Observation

summarise(df,first = first(x1))

Last observation

summarise(df,last = last(x1))

nth observation

summarise(df,nth = nth(x1, 2))

Number of occurrence

summarise(df,count = n(x1))

Number of distinct occurrence

summarise(df,distinct = n_distinct(x1))

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