# How to find the mean of all columns by group in R?

To find the mean of all columns by group, we can use summarise_all function along with mean function after defining the groups with group_by. For example, if we have a data frame called df that contains a grouping column say G and some numerical columns then we can find the mean of all columns by values in grouping column by using the below given command −

df%>%group_by(G)%>%summarise_all("mean")

## Example 1

Following snippet creates a sample data frame −

Grp<-sample(LETTERS[1:4],20,replace=TRUE)
Score1<-sample(1:50,20)
Score2<-sample(1:50,20)
Score3<-sample(1:50,20)
df1<-data.frame(Grp,Score1,Score2,Score3)
df1

The following dataframe is created −

  Grp Score1 Score2 Score3
1  C   2     1      46
2  C  39    25      21
3  C  25     6      10
4  A   5     8      25
5  A  37    23      17
6  D   4    21      39
7  B  33    40      31
8  C  28    44       3
9  B  40    50       8
10 B  10    49      14
11 B  27    45      42
12 B  45     7       5
13 C  26    34      28
14 C  31    19      12
15 A  29    46      38
16 A  24    38      48
17 A  21    12      22
18 B   1     9      35
19 A  23    20      20
20 B  50    27       9

To load dplyr package and find the mean of all columns by Grp column, add the following code to the above snippet −

library(dplyr)
df1%>%group_by(Grp)%>%summarise_all("mean")
# A tibble: 4 x 4

## Outpu

If you execute all the above given snippets as a single program, it generates the following output: −

   Grp  Score1 Score2 Score3
<chr> <dbl>  <dbl> <dbl>
1   A   23.2   24.5  28.3
2   B   29.4   32.4  20.6
3   C   25.2   21.5    20
4   D      4     21    39

## Example 2

Following snippet creates a sample data frame −

Level<-sample(c("First","Second","Third"),20,replace=TRUE)
Price1<-rpois(20,8)
Price2<-rpois(20,8)
Price3<-rpois(20,8)
df2<-data.frame(Level,Price1,Price2,Price3)
df2

The following dataframe is created −

   Level Price1 Price2 Price3
1  First   11    12     5
2  First    8     6     5
3  First    5    16     6
4  Second   9    11     9
5  Second  12    12    11
6  Second   5    10     8
7  First    7     6     9
8  First   10     6    11
9  Second   4     9     8
10 First    5     9     5
11 Third   14     6     8
12 Third    4    13    11
13 Second   3     8     5
14 Second   8     3     8
15 Second   6    10    10
16 Second  10     3     9
17 First    8     8     5
18 First    6     3    11
19 Third    5    10     9
20 Third   10    11    10

To find the mean of all columns by Level column, add the following code to the above snippet −

df2%>%group_by(Level)%>%summarise_all("mean")
# A tibble: 3 x 4

## Output

If you execute all the above given snippets as a single program, it generates the following output: −

  Level  Price1 Price2 Price3
<chr>  <dbl>  <dbl> <dbl>
1 First   7.5   8.25  7.12
2 Second  7.12  8.25  8.5
3 Third   8.25    10  9.5