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Find the column name with the largest value for each row in an R data frame.
To find the column name that has the largest value for each row in an R data frame, we can use colnames function along with apply function.
For Example, if we have a data frame called df then we can find column name that has the largest value for each row by using the command as follows −
df$Largest_Column<-colnames(df)[apply(df,1,which.max)]
Example 1
Following snippet creates a sample data frame −
x1<-rnorm(20) x2<-rnorm(20) x3<-rnorm(20) df1<-data.frame(x1,x2,x3) df1
The following dataframe is created
x1 x2 x3 1 -0.305888032 1.42530072 -0.60397460 2 0.077412581 1.33102088 1.09897001 3 -0.001797155 1.85365113 0.59881492 4 -0.235863387 -0.11476965 -0.23914040 5 0.641954539 -0.80069293 1.78915326 6 1.662750089 -0.48168001 -1.63141513 7 1.393413983 -0.21044222 -0.36966594 8 0.387820650 0.04998259 -0.88707049 9 -0.982245543 -1.04089646 1.51510464 10 1.540251727 -0.24360161 -0.72272136 11 0.871043177 -1.61258877 -0.08300941 12 0.894436819 1.22285505 0.25353571 13 -0.706468609 0.37879788 1.09617879 14 1.366866702 -2.36429211 0.47667869 15 0.827015705 -0.29348558 2.57175974 16 -0.709173752 -0.68338183 -0.15060505 17 0.464121383 -0.41577526 -1.52947993 18 -0.322493725 0.46212973 1.38418790 19 0.588932732 -1.98841476 0.43082069 20 -0.775650742 -0.45247281 0.62378543
To find the column name that has the largest value for each row in df1 on the above created data frame, add the following code to the above snippet −
x1<-rnorm(20) x2<-rnorm(20) x3<-rnorm(20) df1<-data.frame(x1,x2,x3) df1$Largest_Column<-colnames(df1)[apply(df1,1,which.max)] df1
Output
If you execute all the above given snippets as a single program, it generates the following Output −
x1 x2 x3 Largest_Column 1 -0.305888032 1.42530072 -0.60397460 x2 2 0.077412581 1.33102088 1.09897001 x2 3 -0.001797155 1.85365113 0.59881492 x2 4 -0.235863387 -0.11476965 -0.23914040 x2 5 0.641954539 -0.80069293 1.78915326 x3 6 1.662750089 -0.48168001 -1.63141513 x1 7 1.393413983 -0.21044222 -0.36966594 x1 8 0.387820650 0.04998259 -0.88707049 x1 9 -0.982245543 -1.04089646 1.51510464 x3 10 1.540251727 -0.24360161 -0.72272136 x1 11 0.871043177 -1.61258877 -0.08300941 x1 12 0.894436819 1.22285505 0.25353571 x2 13 -0.706468609 0.37879788 1.09617879 x3 14 1.366866702 -2.36429211 0.47667869 x1 15 0.827015705 -0.29348558 2.57175974 x3 16 -0.709173752 -0.68338183 -0.15060505 x3 17 0.464121383 -0.41577526 -1.52947993 x1 18 -0.322493725 0.46212973 1.38418790 x3 19 0.588932732 -1.98841476 0.43082069 x1 20 -0.775650742 -0.45247281 0.62378543 x3
Example 2
Following snippet creates a sample data frame −
y1<-rpois(20,5) y2<-rpois(20,5) y3<-rpois(20,5) y4<-rpois(20,5) df2<-data.frame(y1,y2,y3,y4) df2
The following dataframe is created
y1 y2 y3 y4 1 4 5 4 8 2 6 6 8 5 3 4 7 5 4 4 8 2 7 7 5 3 6 5 0 6 4 5 4 7 7 6 1 2 9 8 5 4 3 5 9 9 5 6 5 10 8 3 7 9 11 5 14 7 5 12 4 7 4 4 13 9 3 1 2 14 5 8 9 4 15 2 7 2 5 16 4 3 3 5 17 4 6 4 4 18 7 6 4 4 19 12 6 8 4 20 6 6 4 5
To find the column name that has the largest value for each row in df2 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) y4<-rpois(20,5) df2<-data.frame(y1,y2,y3,y4) df2$Largest_Col<-colnames(df2)[apply(df2,1,which.max)] df2
Output
If you execute all the above given snippets as a single program, it generates the following Output −
y1 y2 y3 y4 Largest_Col 1 4 5 4 8 y4 2 6 6 8 5 y3 3 4 7 5 4 y2 4 8 2 7 7 y1 5 3 6 5 0 y2 6 4 5 4 7 y4 7 6 1 2 9 y4 8 5 4 3 5 y1 9 9 5 6 5 y1 10 8 3 7 9 y4 11 5 14 7 5 y2 12 4 7 4 4 y2 13 9 3 1 2 y1 14 5 8 9 4 y3 15 2 7 2 5 y2 16 4 3 3 5 y4 17 4 6 4 4 y2 18 7 6 4 4 y1 19 12 6 8 4 y1 20 6 6 4 5 y1
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