How to change the column names in R within aggregate function?

The column names in an R data frame are an important part of the data because by reading the column names any viewer is likely to understand the theoretical background behind it. If that name is not appropriate then we might want to change it. While using the aggregate function to calculate mean or any other statistical summary, it is possible to change that name with another name by defining the new name with list.

Example

Consider the below data frame −

set.seed(1)
x1<-rnorm(100)
x2<-rep(c(LETTERS[1:25]),times=4)
df<-data.frame(x1,x2)
head(df,20)
    x1       x2
1  -0.62645381 A
2   0.18364332 B
3  -0.83562861 C
4   1.59528080 D
5   0.32950777 E
6  -0.82046838 F
7   0.48742905 G
8   0.73832471 H
9   0.57578135 I
10 -0.30538839 J
11  1.51178117 K
12  0.38984324 L
13 -0.62124058 M
14 -2.21469989 N
15  1.12493092 O
16 -0.04493361 P
17 -0.01619026 Q
18  0.94383621 R
19  0.82122120 S
20  0.59390132 T
tail(df,20)
      x1      x2
81  -0.5686687 F
82  -0.1351786 G
83   1.1780870 H
84  -1.5235668 I
85   0.5939462 J
86   0.3329504 K
87   1.0630998 L
88  -0.3041839 M
89   0.3700188 N
90   0.2670988 O
91  -0.5425200 P
92   1.2078678 Q
93   1.1604026 R
94   0.7002136 S
95   1.5868335 T
96   0.5584864 U
97  -1.2765922 V
98  -0.5732654 W
99  -1.2246126 X
100 -0.4734006 Y

Changing the name of columns inside aggregate function with mean −

new_df <- aggregate(list(One=df$x1),list(Two=df$x2),mean)
head(new_df)
  Two One
1 A  0.001742391
2 B -0.256867612
3 C -0.491038988
4 D  0.015527244
5 E  0.397738022
6 F  0.487485583
new_df
 Two One
1  A  0.001742391
2  B -0.256867612
3  C -0.491038988
4  D  0.015527244
5  E  0.397738022
6  F  0.487485583
7  G -0.029439692
8  H  0.314987172
9  I -0.107967715
10 J -0.305889090
11 K  0.957838684
12 L  0.254853279
13 M -0.073749635
14 N -0.179163387
15 O  0.352983062
16 P -0.140796234
17 Q -0.216660692
18 R  1.066689266
19 S  0.557837845
20 T  0.916147688
21 U  0.311369542
22 V -0.209955094
23 W  0.220139712
24 X -1.065102039
25 Y -0.056525141