CODEWITHSUNDEEP
rmatrix
user3067923
user3067923

Reputation: 457

subset matrix by more than one thing fast

I have a matrix I would like to subset quickly using two criteria. 1) the colnames match the rownames and 2) the value in one matrix is FALSE

m
  [,1]
A    1
B    2
C    3
D    4
E    5

tf
        E     B     A
[1,] FALSE FALSE TRUE

the output should be

m2
  [,1]
E    5
B    2

Upvotes: 1

Views: 62

Answers (1)

akrun
akrun

Reputation: 887501

As there is only a single row for 'tf', when we subset the logical matrix by negating, it results in a named vector as subsetting ([) by default is drop=TRUE. Extract the names from the vector and use it as row index to subset the 'm'. Here, we can use drop=FALSE as there is only a single column in 'm'. 

m[names(tf[,!tf]), , drop=FALSE]
#   [,1]
#E    5
#B    2

data

m <- matrix(1:5, nrow=5, 1, dimnames=list(LETTERS[1:5], NULL))
tf <- matrix(c(FALSE, FALSE, TRUE), ncol=3, dimnames=list(NULL, c("E", "B", "A")))

Upvotes: 2

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