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How to delete matrix rows if a particular column value satisfies some condition in R?
To delete matrix rows if a particular column satisfies some condition, we can use subsetting with single square brackets and take the subset of the matrix based on the condition. For example, if we have a matrix M and want to delete rows if column first of M do not contain value 5 then we can use the command M[M[,1]==5,].
Example
Consider the below matrix −
M1<-matrix(rpois(80,2),ncol=4) M1
Output
[,1] [,2] [,3] [,4] [1,] 1 1 5 4 [2,] 5 2 3 1 [3,] 2 4 4 2 [4,] 1 0 0 2 [5,] 1 6 2 0 [6,] 2 1 2 1 [7,] 1 3 4 2 [8,] 3 1 1 0 [9,] 1 2 2 2 [10,] 0 0 0 1 [11,] 2 1 2 3 [12,] 1 2 4 1 [13,] 1 3 1 1 [14,] 3 3 1 2 [15,] 2 1 2 1 [16,] 2 0 2 1 [17,] 5 2 2 3 [18,] 0 0 0 0 [19,] 2 2 6 1 [20,] 3 1 1 0
Deleting rows of M1 if first value does not contain 2 −
Example
M1[M1[,1]==2,]
Output
[,1] [,2] [,3] [,4] [1,] 2 4 4 2 [2,] 2 1 2 1 [3,] 2 1 2 3 [4,] 2 1 2 1 [5,] 2 0 2 1 [6,] 2 2 6 1
Example
M2<-matrix(rpois(80,1),ncol=4) M2
Output
[,1] [,2] [,3] [,4] [1,] 0 3 2 2 [2,] 0 1 1 0 [3,] 0 0 0 3 [4,] 5 0 3 0 [5,] 0 1 0 1 [6,] 0 0 3 2 [7,] 1 0 0 1 [8,] 0 1 1 2 [9,] 1 1 2 1 [10,] 2 2 1 0 [11,] 1 0 2 0 [12,] 1 0 3 1 [13,] 1 1 0 0 [14,] 2 0 3 1 [15,] 1 0 1 1 [16,] 2 2 0 1 [17,] 1 0 0 2 [18,] 0 1 2 2 [19,] 1 1 5 0 [20,] 2 2 2 0
Deleting rows of M2 if first value contain 0 −
Example
M2[M2[,1]!=0,]
Output
[,1] [,2] [,3] [,4] [1,] 5 0 3 0 [2,] 1 0 0 1 [3,] 1 1 2 1 [4,] 2 2 1 0 [5,] 1 0 2 0 [6,] 1 0 3 1 [7,] 1 1 0 0 [8,] 2 0 3 1 [9,] 1 0 1 1 [10,] 2 2 0 1 [11,] 1 0 0 2 [12,] 1 1 5 0 [13,] 2 2 2 0
Updated on: 17-Mar-2021
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