[R] how to find indices of particular array elements

[Martin Lam]

# create a 4x4 matrix with random values
smallmatrix = matrix(runif(16)*10, ncol = 4, nrow = 4)

# get the row and column number of the item in the
matrix with the highest value
which(smallmatrix == max(smallmatrix), arr.ind = 1)

HTH,

Martin

--- Jonathan Williams
<jonathan.williams at pharmacology.oxford.ac.uk> wrote:

> Dear R helpers,
> 
> I have a largish matrix (1300 x 1300) and I wish to
> find the row and column
> numbers that identify particular elements whose
> values I know in advance
> (for example, the row and column numbers for the
> maximum value of the
> matrix).
> 
> I have looked in the help manual and found the
> functions 'row' and 'col' for
> finding the indices of a matrix. But, I can't figure
> out how to use them to
> obtain the indices of the matrix element with
> maximum value, despite over an
> hour of trying!
> 
> Many thanks for your help,
> 
> Jonathan Williams
> 
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