How to create an empty matrix in R

Question

I am new to R  I want to fill in an empty matrix with the results of my for loop using cbind  My question is  how can I eliminate the NAs in the first column of my matrix  I include my code below    output lt -matrix  15     generate an empty matrix with 15 rows  the first column already filled with NAs  is there any way to leave the first column empty   for  enter code here      normF lt - enter code here    output lt -cbind output normF      The output is the matrix I expected  The only issue is that its first column is filled with NAs  How can I delete those NAs

User · Answer

I d be cautious as dismissing something as a bad idea because it is slow  If it is a part of the code that does not take much time to execute then the slowness is irrelevant  I just used the following code   for  ic in 1  dim centroid  2      cluster  ic   matrix  nrow 2 ncol 0      code to identify cluster pindex ip  to which to add the point if pdist ip  gt -1    cluster  pindex ip    cbind cluster  pindex ip    points  ip       for a problem that ran in less than 1 second

User · Answer

To get rid of the first column of NAs  you can do it with negative indexing  which removes indices from the R data set    For example   output   matrix 1 6  2  3    gives you a 2 x 3 matrix filled with the numbers 1 to 6    output                  1    2    3         1      1    3    5        2      2    4    6  output   output  -1    this removes column 1 for all rows    output                  1    2         1      3    5        2      4    6   So you can just add output   output  -1 after the for loop in your original code

User · Answer

If you don t know the number of columns ahead of time  add each column to a list and cbind at the end   List  lt - list   for i in 1 n        normF  lt -  something     List  i    lt - normF   Matrix   do call cbind  List

User · Answer

The default for matrix is to have 1 column   To explicitly have 0 columns  you need to write  matrix   nrow   15  ncol   0    A better way would be to preallocate the entire matrix and then fill it in  mat  lt - matrix   nrow   15  ncol   n columns  for column in 1 n columns     mat   column   lt - vector

[r] How to create an empty matrix in R?

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