Syntax error How to recode factors in R?

How to recode factors in R?

Sometimes we have factor levels that can be combined or we want to group those levels in a single level. It is mostly done in situations where we have only one value for a particular factor level or there exists some theoretical concept that leads to combining the factor levels. For example, if we have a data frame called df that contains a factor column say x having four categories A, B, C, and D then they can be grouped into A and B as −

df$x[df$x %in% c("A","B")]<-"A"
df$x[df$x %in% c("C","D")]<-"B"

Example

Consider the below data frame −

 Live Demo

factor<-sample(LETTERS[1:4],20,replace=TRUE)
response<-rpois(20,5)
df1<-data.frame(factor,response)
df1

Output

   factor response
1  A      5
2  C      7
3  D      5
4  C     13
5  C      5
6  C      4
7  B      4
8  B     10
9  C      4
10 D      6
11 B      5
12 B      3
13 A      7
14 A      2
15 A      2
16 D      3
17 B      1
18 C      5
19 D      6
20 D      4

Recoding factor levels in factor column of df1 −

df1$factor[df1$factor %in% c("A","B")]<-"A"
df1$factor[df1$factor %in% c("C","D")]<-"B"
df1

Output

 factor response
1  A     5
2  B     7
3  B     5
4  B    13
5  B     5
6  B     4
7  A     4
8  A    10
9  B     4
10 B     6
11 A     5
12 A     3
13 A     7
14 A     2
15 A     2
16 B     3
17 A     1
18 B     5
19 B     6
20 B     4

Example2

 Live Demo

grp<-sample(c("G1","G2","G3"),20,replace=TRUE)
Y<-rnorm(20)
df2<-data.frame(grp,Y)
df2

Output

   grp     Y
1  G3  -0.39900138
2  G3   1.04085657
3  G1   1.46432790
4  G3  -0.90843955
5  G1  -0.15202516
6  G2   1.15456629
7  G2   1.24002828
8  G2  -1.10731484
9  G2   0.27423208
10 G3   1.06444903
11 G2  -0.21824650
12 G1   0.25843090
13 G1   0.07686889
14 G3  -0.21955611
15 G3  -0.05359245
16 G2   0.54630987
17 G3  -0.09808820
18 G1  -0.65171471
19 G2  -0.62371231
20 G2  -0.03319190

Recoding factor levels in grp column of df2 −

df2$grp[df2$grp %in% c("G1","G2")]<-"Control"
df2
    grp      Y
1  G3      -0.39900138
2  G3       1.04085657
3  Control  1.46432790
4  G3      -0.90843955
5  Control -0.15202516
6  Control  1.15456629
7  Control  1.24002828
8  Control -1.10731484
9  Control  0.27423208
10 G3       1.06444903
11 Control -0.21824650
12 Control  0.25843090
13 Control  0.07686889
14 G3      -0.21955611
15 G3      -0.05359245
16 Control  0.54630987
17 G3      -0.09808820
18 Control -0.65171471
19 Control -0.62371231
20 Control -0.03319190
Updated on: 2021-03-06T13:23:43+05:30

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