Find the column name of least value in each row of an R dataframe.

To find the column name that has the least 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 least value for each row by using the command mentioned below −

df$Least_Column<-colnames(df)[apply(df,1,which.min)]

Example 1

Following snippet creates a sample data frame −

x1<-rpois(20,10) x2<-rpois(20,10) x3<-rpois(20,10) x4<-rpois(20,10) df1<-data.frame(x1,x2,x3,x4) df1

The following dataframe is created

  x1  x2 x3 x4 1  6  12 9 8 2 15  16 9 9 3  8   7 11 10 4 13   8 8 9 5 14  10 15 15 6  5  10 4 10 7 10  13 5 9 8  7   7 9 12 9  9  14 11 8 10 6   9 6 10 11 12 12 10 12 12  8  4 12 9 13  8  9 15 14 14 14  9 8 6 15 10 15 12 12 16 13  9 8 13 17 11 15 7 11 18 11 13 9 7 19 14  8 12 6 20  7  6 13 10

To find the column name that has the least value for each row in df1 on the above created data frame, add the following code to the above snippet −

x1<-rpois(20,10) x2<-rpois(20,10) x3<-rpois(20,10) x4<-rpois(20,10) df1<-data.frame(x1,x2,x3,x4) df1$Smallest_Col<-colnames(df1)[apply(df1,1,which.min)] df1

Output

If you execute all the above given snippets as a single program, it generates the following Output −

    x1  x2 x3 x4 Smallest_Col 1   6  12  9  8   x1 2  15  16  9  9   x3 3   8   7 11 10   x2 4  13   8  8  9   x2 5  14  10 15 15   x2 6   5  10  4 10   x3 7  10  13  5  9   x3 8   7   7  9 12   x1 9   9  14 11  8   x4 10  6   9  6 10   x1 11 12  12 10 12   x3 12  8   4 12  9   x2 13  8   9 15 14   x1 14 14   9  8  6   x4 15 10  15 12 12   x1 16 13   9  8 13   x3 17 11  15  7 11   x3 18 11  13  9  7   x4 19 14   8 12  6   x4 20  7   6 13  10 x2

Example 2

Following snippet creates a sample data frame −

y1<-round(rnorm(20),2) y2<-round(rnorm(20),2) y3<-round(rnorm(20),2) df2<-data.frame(y1,y2,y3) df2

The following dataframe is created

 y1 y2 y3 1 -0.33 0.19 -0.18 2 -1.41 -0.42 -0.06 3 -0.48 -0.62 -0.51 4 -0.27 0.68 0.38 5 1.00 1.04 1.31 6 -0.29 0.04 -1.23 7 0.65 -1.47 -1.11 8 0.33 0.14 0.80 9 1.29 0.20 1.14 10 -0.26 0.10 0.64 11 0.42 -0.17 0.64 12 -0.31 1.53 -0.41 13 0.21 -0.87 -1.03 14 0.85 1.82 -1.35 15 0.80 0.89 0.45 16 0.65 1.08 0.08 17 -0.05 -1.16 0.35 18 -0.91 -0.19 -0.93 19 0.14 -1.30 -0.91 20 -0.03 2.02 1.41

To find the column name that has the least value for each row in df2 on the above created data frame, add the following code to the above snippet −

y1<-round(rnorm(20),2) y2<-round(rnorm(20),2) y3<-round(rnorm(20),2) df2<-data.frame(y1,y2,y3) df2$Smallest_Col<-colnames(df2)[apply(df2,1,which.min)] df2

Output

If you execute all the above given snippets as a single program, it generates the following Output −

      y1 y2 y3 Smallest_Col  1 -0.33  0.19 -0.18 y1  2 -1.41 -0.42 -0.06 y1  3 -0.48 -0.62 -0.51 y2  4 -0.27  0.68 0.38 y1  5  1.00  1.04 1.31 y1  6 -0.29 0.04 -1.23 y3  7  0.65 -1.47 -1.11 y2  8  0.33 0.14 0.80 y2  9  1.29 0.20 1.14 y2 10 -0.26 0.10 0.64 y1 11  0.42 -0.17 0.64 y2 12 -0.31 1.53 -0.41 y3 13  0.21 -0.87 -1.03 y3 14  0.85 1.82 -1.35 y3 15  0.80 0.89 0.45 y3 16  0.65 1.08 0.08 y3 17 -0.05 -1.16 0.35 y2 18 -0.91 -0.19 -0.93 y3 19  0.14 -1.30 -0.91 y2 20 -0.03 2.02 1.41 y1