Re: [R] Row names and matrixs

From: jlemaitre <josh_at_richrelevance.com>
Date: Thu, 12 May 2011 14:58:11 -0700 (PDT)

Nielsen,
The numbers in the brackets reference a component of a matrix/data frame/vector. So if you have:
> x <- c(1:10) # a vector of integers in sequence from 1-10 > x[3] # the third component of x
[1] 3

For 2-way matrices or data frames, the formatting is [row,column]. So, for a 10 x 10 matrix x:
> x <- matrix(1:100, ncol = 10, byrow = T) > x

      [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
[1,] 1 2 3 4 5 6 7 8 9 10
[2,] 11 12 13 14 15 16 17 18 19 20
[3,] 21 22 23 24 25 26 27 28 29 30
[4,] 31 32 33 34 35 36 37 38 39 40
[5,] 41 42 43 44 45 46 47 48 49 50
[6,] 51 52 53 54 55 56 57 58 59 60
[7,] 61 62 63 64 65 66 67 68 69 70
[8,] 71 72 73 74 75 76 77 78 79 80
[9,] 81 82 83 84 85 86 87 88 89 90
[10,] 91 92 93 94 95 96 97 98 99 100

> x[,1] # return the first column of x
[1] 1 11 21 31 41 51 61 71 81 91

> x[1,] # return the first row of x
[1] 1 2 3 4 5 6 7 8 9 10

when there's a minus, it just means that component is omitted

> x[-1,] # return x less the first row

      [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
[1,] 11 12 13 14 15 16 17 18 19 20
[2,] 21 22 23 24 25 26 27 28 29 30
[3,] 31 32 33 34 35 36 37 38 39 40
[4,] 41 42 43 44 45 46 47 48 49 50
[5,] 51 52 53 54 55 56 57 58 59 60
[6,] 61 62 63 64 65 66 67 68 69 70
[7,] 71 72 73 74 75 76 77 78 79 80
[8,] 81 82 83 84 85 86 87 88 89 90
[9,] 91 92 93 94 95 96 97 98 99 100

Given this context, I would double check the contents of test vs. test1. And don't let arrogant posts on this help forum discourage you. I hope this helps.

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Received on Thu 12 May 2011 - 22:37:00 GMT

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