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R Programming to find the column name for row maximum in a data.table object.
If we have a data.table object and we want to find the column name for row maximum then we can use max.col function.
For Example, if we have a data.table object called DT then we can find the column name for row maximum by using the below command −
DT[,names(.SD)[max.col(.SD,ties.method="first")]]
Example 1
Following snippet creates a sample data frame −
x1<-round(rnorm(20),2) x2<-round(rnorm(20),2) x3<-round(rnorm(20),2) x4<-round(rnorm(20),2) DT1<-data.table(x1,x2,x3,x4) DT1
The following dataframe is created
x1 x2 x3 x4 1: 0.10 -0.77 0.01 -0.28 2: -0.81 -0.88 -1.25 -1.03 3: -0.43 1.24 1.27 0.59 4: 1.55 -0.71 0.21 -0.16 5: 1.50 -0.80 0.26 0.32 6: -0.74 -0.19 0.11 -2.21 7: -0.12 1.17 -0.08 1.63 8: 1.16 -2.45 0.40 -0.49 9: -0.42 0.49 -1.43 1.14 10: -0.63 0.79 1.39 -2.28 11: 1.03 0.79 2.10 0.85 12: -1.07 -1.50 2.45 0.05 13: 0.62 -0.25 -0.11 0.50 14: -0.32 1.23 -0.92 1.13 15: -1.14 1.95 -0.36 -0.77 16: -1.15 -0.24 0.59 0.89 17: 2.03 -1.10 1.74 -1.96 18: -0.06 1.47 0.11 1.64 19: -2.13 1.45 -1.64 -0.71 20: 1.37 -0.41 -0.21 0.37
To find the column name for row maximum in DT1 on the above created data frame, add the following code to the above snippet −
x1<-round(rnorm(20),2) x2<-round(rnorm(20),2) x3<-round(rnorm(20),2) x4<-round(rnorm(20),2) DT1<-data.table(x1,x2,x3,x4) DT1[,names(.SD)[max.col(.SD,ties.method="first")]]
Output
If you execute all the above given snippets as a single program, it generates the following Output −
[1] "x1" "x1" "x3" "x1" "x1" "x3" "x4" "x1" "x4" "x3" "x3" "x3" "x1" "x2" "x2" [16] "x4" "x1" "x4" "x2" "x1"
Example 2
Following snippet creates a sample data frame −
y1<-rpois(20,5) y2<-rpois(20,5) y3<-rpois(20,5) DT2<-data.table(y1,y2,y3) DT2
The following dataframe is created
y1 y2 y3 1: 5 4 4 2: 3 5 4 3: 3 6 6 4: 8 4 7 5: 1 11 8 6: 11 5 7 7: 3 5 7 8: 5 9 8 9: 4 6 4 10: 4 3 2 11: 2 6 4 12: 4 5 3 13: 7 9 7 14: 6 12 3 15: 4 10 5 16: 5 5 3 17: 7 6 4 18: 3 2 3 19: 6 3 3 20: 1 2 5
To find the column name for row maximum in DT2 on the above created data frame, add the following code to the above snippet −
y1<-rpois(20,5) y2<-rpois(20,5) y3<-rpois(20,5) DT2<-data.table(y1,y2,y3) DT2 DT2[,names(.SD)[max.col(.SD,ties.method="first")]]
Output
If you execute all the above given snippets as a single program, it generates the following Output −
[1] "y1" "y2" "y2" "y1" "y2" "y1" "y3" "y2" "y2" "y1" "y2" "y2" "y2" "y2" "y2" [16] "y1" "y1" "y1" "y1" "y3"
Example 3
Following snippet creates a sample data frame −
z1<-rexp(20) z2<-rexp(20) z3<-rexp(20) DT3<-data.table(z1,z2,z3) DT3
The following dataframe is created
z1 z2 z3 1: 1.85175520 0.06988659 0.10876221 2: 1.69589804 0.83393956 0.08359516 3: 4.53698884 0.14180505 0.77873494 4: 1.61637232 0.40584249 0.59490613 5: 0.96935637 0.24492793 0.47872486 6: 1.81591399 0.75036377 0.10156744 7: 0.65936883 0.22916612 1.38184152 8: 0.71911018 0.11860198 1.03305886 9: 0.01083114 7.64524696 0.07793300 10: 0.62813099 1.35159142 0.28918956 11: 0.32457686 0.02591335 5.85365604 12: 0.42783663 1.21874776 0.38176176 13: 1.16153548 0.24340230 0.42469609 14: 1.58644074 0.51814087 0.50409917 15: 1.21327299 1.73146461 0.89982450 16: 0.51891446 0.47827326 0.06424925 17: 0.60590047 0.29575678 0.16249550 18: 0.39925252 0.02687194 0.52659081 19: 1.15769384 1.76426512 0.34584972 20: 0.06939622 0.37072691 0.23280432
To find the column name for row maximum in DT3 on the above created data frame, add the following code to the above snippet −
z1<-rexp(20) z2<-rexp(20) z3<-rexp(20) DT3<-data.table(z1,z2,z3) DT3[,names(.SD)[max.col(.SD,ties.method="first")]]
Output
If you execute all the above given snippets as a single program, it generates the following Output −
[1] "z1" "z1" "z1" "z1" "z1" "z1" "z3" "z3" "z2" "z2" "z3" "z2" "z1" "z1" "z2" [16] "z1" "z1" "z3" "z2" "z2"
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