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How can I select, say top 100 rows of a matrix in R? All I found is using subset which requires condition parameter. All I need to make smaller matrix by using only first n number of rows with same number of columns
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If you want to select all elements of a row or a column, no number is needed before or after the comma, respectively: my_matrix[,1] selects all elements of the first column. my_matrix[1,] selects all elements of the first row.
To take a random sample from a matrix in R, we can simply use sample function and if the sample size is larger than the number of elements in the matrix replace=TRUE argument will be used.
To print the first row use l[0] , to get columns you will need to transpose with zip print(list(zip(*l))[0]) .
An asterisk is occasionally used to refer to whole rows or columns in a matrix. For example, ai,∗ refers to the ith row of A, and a∗,j refers to the jth column of A.
Use the head function:
head(mat, 100)
The simplest way to do it would be a[1:100,] (unless there are fewer than 100 rows, in which case head(a,100) works better)
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