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# How to find the index of values in matrix column in R if they occur once?

To find the index of values in R matrix column if they occur once, we can follow the below steps −

First of all, create a matrix.

Then, use which function along with duplicated function and single square brackets for subsetting to find the index of values in a column if they occur once.

## Example 1

#### Create the data frame

Let’s create a data frame as shown below −

M1<-matrix(rpois(25,10),ncol=1) M1

## Output

On executing, the above script generates the below output(this output will vary on your system due to randomization) −

[,1] [1,] 13 [2,] 6 [3,] 12 [4,] 8 [5,] 12 [6,] 5 [7,] 11 [8,] 8 [9,] 11 [10,] 12 [11,] 16 [12,] 11 [13,] 15 [14,] 5 [15,] 11 [16,] 9 [17,] 12 [18,] 9 [19,] 8 [20,] 7 [21,] 9 [22,] 7 [23,] 15 [24,] 14 [25,] 9

**Find the index of values in a column if they occur once**

Using which function along with duplicated function and single square brackets for subsetting to find the index of values in the column of matrix M1 if they occur once −

M1<-matrix(rpois(25,10),ncol=1) which(!(M1[] %in% M1[][duplicated(M1[])]))

## Output

[1] 9 20 21

## Example 2

#### Create the data frame

Let’s create a data frame as shown below −

M2<-matrix(round(rnorm(25),1),ncol=1) M2

## Output

On executing, the above script generates the below output(this output will vary on your system due to randomization) −

[,1] [1,] 1.7 [2,] -1.0 [3,] -1.1 [4,] 0.8 [5,] 0.7 [6,] 0.7 [7,] 1.9 [8,] -1.6 [9,] 2.7 [10,] 0.9 [11,] -0.6 [12,] 1.0 [13,] -2.1 [14,] -1.1 [15,] 1.4 [16,] 0.2 [17,] -0.7 [18,] 1.4 [19,] 0.6 [20,] -0.6 [21,] 0.0 [22,] -0.1 [23,] 0.6 [24,] 0.5 [25,] -0.9

**Find the index of values in a column if they occur once**

Using which function along with duplicated function and single square brackets for sub setting to find the index of values in the column of matrix M2 if they occur once −

M2<-matrix(round(rnorm(25),1),ncol=1) which(!(M2[] %in% M2[][duplicated(M2[])]))

## Output

[1] 2 3 6 7 10 12 14 16 17 18 19 21 23

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