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How to find the groupwise common value for a data.table object?
To find the groupwise common value for a data.table object, we can use Reduce function with intersect function.
For example, if we have a data.table object called DT that contains a numerical column say Num and a categorical column say C where C exists at the first position then the groupwise common value can be found by using the command given below −
Reduce(intersect,DT[,.(list(unique(Num))),C]$V1)
Example
Consider the below data.table object −
Group<-sample(LETTERS[1:4],20,replace=TRUE) Rate<-rpois(20,1) library(data.table) DT1<-data.table(Group,Rate) DT1
output
The following dataframe is created −
Group Rate 1: A 4 2: C 0 3: D 0 4: C 0 5: A 3 6: A 1 7: D 1 8: B 0 9: A 1 10: A 0 11: C 3 12: B 2 13: B 1 14: C 2 15: D 3 16: B 1 17: A 0 18: C 1 19: A 1 20: C 1
In order to find the groupwise common value of Rate for all groups in Group column, add the following code to the above snippet −
Example
Reduce(intersect,DT1[,.(list(unique(Rate))),Group]$V1)
Output
If you execute all the above given snippets as a single program, it generates the following Output −
[1] 1 0
Example
Consider the below data.table object −
Category<-sample(c("I","II","III"),20,replace=TRUE)
Rank<-sample(1:3,20,replace=TRUE)
DT2<-data.table(Category,Rank)
DT2output
The following dataframe is created −
Category Rank 1: I 1 2: III 2 3: III 3 4: I 2 5: I 3 6: III 3 7: III 2 8: III 2 9: III 2 10: II 3 11: III 2 12: II 1 13: III 1 14: II 3 15: I 1 16: III 2 17: III 1 18: II 1 19: I 1 20: III 3
To find the groupwise common value of Rank for all groups in Category column, add the following code to the above snippet −
Example
Reduce(intersect,DT2[,.(list(unique(Rank))),Category]$V1)
Output
If you execute all the above given snippets as a single program, it generates the following Output −
[1] 1 3
Example
Consider the below data.table object −
Class<-sample(c("First","Second","Third"),20,replace=TRUE)
Score<-sample(0:2,20,replace=TRUE)
DT3<-data.table(Class,Score)
DT3output
The following dataframe is created −
Class Score 1: First 2 2: Second 0 3: First 1 4: Third 2 5: Second 1 6: Third 1 7: Third 0 8: Third 1 9: Third 2 10: Third 1 11: Second 0 12: Third 0 13: First 2 14: First 1 15: First 1 16: First 0 17: Second 2 18: Second 2 19: First 0 20: Second 1
To find the groupwise common value of Score for all groups in Class column, add the following code to the above snippet −
Example
Reduce(intersect,DT3[,.(list(unique(Score))),Class]$V1)
Output
If you execute all the above given snippets as a single program, it generates the following Output −
[1] 2 1 0
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