How to extract columns based on particular column values of an R data frame that match\\na pattern?

The column values of an R data frame can be easily extracted by subsetting with single square brackets but if we want to extract the column values that match a pattern then we need to use grepl function inside single square brackets, this will help us to match the pattern of the values in the data frame columns.

Example

Consider the below data frame:

Live Demo

> set.seed(271) > x1<-sample(c("A187","A321","A123","A242"),20,replace=TRUE) > x2<-sample(c("B87","B74","B81","B71"),20,replace=TRUE) > df1<-data.frame(x1,x2) > df1

Output

 x1 x2 1 A242 B71 2 A123 B71 3 A242 B81 4 A242 B87 5 A123 B71 6 A321 B71 7 A187 B74 8 A321 B74 9 A123 B71 10 A242 B74 11 A321 B74 12 A187 B87 13 A321 B74 14 A321 B74 15 A123 B74 16 A187 B87 17 A123 B81 18 A242 B87 19 A242 B71 20 A187 B74

Extracting values that starts with A1:

Example

> df1[grepl("A1",x1),]

Output

x1 x2 2 A123 B71 5 A123 B71 7 A187 B74 9 A123 B71 12 A187 B87 15 A123 B74 16 A187 B87 17 A123 B81 20 A187 B74

Extracting values that starts with A2:

Example

> df1[grepl("A2",x1),]

Output

 x1 x2 1 A242 B71 3 A242 B81 4 A242 B87 10 A242 B74 18 A242 B87 19 A242 B71

Extracting values that starts with A3:

Example

> df1[grepl("A3",x1),]

Output

 x1 x2 6 A321 B71 8 A321 B74 11 A321 B74 13 A321 B74 14 A321 B74

Extracting values that starts with B7:

Example

> df1[grepl("B7",x2),]

Output

 x1 x2 1 A242 B71 2 A123 B71 5 A123 B71 6 A321 B71 7 A187 B74 8 A321 B74 9 A123 B71 10 A242 B74 11 A321 B74 13 A321 B74 14 A321 B74 15 A123 B74 19 A242 B71 20 A187 B74

Extracting values that starts with B8:

Example

> df1[grepl("B8",x2),]

Output

 x1 x2 3 A242 B81 4 A242 B87 12 A187 B87 16 A187 B87 17 A123 B81 18 A242 B87

Let’s have a look at another example:

Example

Live Demo

> y1<-sample(c("ID1","ID2","ID3","ID4"),20,replace=TRUE) > y2<-sample(c("C1","C2"),20,replace=TRUE) > df2<-data.frame(y1,y2) > df2

Output

 y1 y2 1 ID1 C1 2 ID3 C1 3 ID1 C1 4 ID2 C2 5 ID4 C2 6 ID2 C2 7 ID2 C1 8 ID3 C1 9 ID1 C1 10 ID1 C1 11 ID2 C2 12 ID2 C2 13 ID4 C1 14 ID3 C2 15 ID2 C1 16 ID4 C1 17 ID4 C1 18 ID2 C2 19 ID2 C2 20 ID3 C2

Example

> df2[grepl("ID1",y1),]

Output

 y1 y2 1 ID1 C1 3 ID1 C1 9 ID1 C1 10 ID1 C1

Example

> df2[grepl("ID2",y1),]

Output

 y1 y2 4 ID2 C2 6 ID2 C2 7 ID2 C1 11 ID2 C2 12 ID2 C2 15 ID2 C1 18 ID2 C2 19 ID2 C2

Example

> df2[grepl("ID3",y1),]

Output

 y1 y2 2 ID3 C1 8 ID3 C1 14 ID3 C2 20 ID3 C2

Example

> df2[grepl("ID4",y1),]

Output

 y1 y2 5 ID4 C2 13 ID4 C1 16 ID4 C1 17 ID4 C1

Example

> df2[grepl("C1",y2),]

Output

 y1 y2 1 ID1 C1 2 ID3 C1 3 ID1 C1 7 ID2 C1 8 ID3 C1 9 ID1 C1 10 ID1 C1 13 ID4 C1 15 ID2 C1 16 ID4 C1 17 ID4 C1

Example

> df2[grepl("C2",y2),]

Output

 y1 y2 4 ID2 C2 5 ID4 C2 6 ID2 C2 11 ID2 C2 12 ID2 C2 14 ID3 C2 18 ID2 C2 19 ID2 C2 20 ID3 C2