# [R] 'matrix' returns integer instead of decimal

From: Brant Inman <brant.inman_at_gmail.com>
Date: Sun, 20 Jan 2008 21:00:59 -0600

R-helpers:

I am experiencing some odd behavior with the 'matrix' function that I have not experienced before and was wondering if there is something that I was missing in my code.

> sessionInfo()
R version 2.6.1 (2007-11-26)
i386-pc-mingw32
locale:
LC_COLLATE=English_United States.1252;LC_CTYPE=English_United States.1252;LC_MONETARY=English_United
States.1252;LC_NUMERIC=C;LC_TIME=English_United States.1252  attached base packages:
[1] splines grid stats graphics grDevices utils datasets
methods
[9] base

other attached packages:
[1] meta_0.8-2 car_1.2-7 arm_1.1-1 R2WinBUGS_2.1-6

[5] coda_0.13-1 lme4_0.99875-9 Matrix_0.999375-3 nlme_3.1-86

[13] foreign_0.8-23 RGraphics_1.0-6 lattice_0.17-4
loaded via a namespace (and not attached):
[1] rcompgen_0.1-17 tools_2.6.1

> rm(list=ls())

```> matrix(c(7,47,4,38,20,96,1,14,10,48,2,101,12,161,     # Make a data matrix
+ 1,28,1,19,22,49,25,162,31,200,9,39,22,193,
+ 0.5,45.5,31,131,4,75,31,220,7,55,3,91,14.5,
+ 25.5,3,65,25,54,24,41,37,95,11,17,26,49,13,
+ 84,38,170,29,60,9,20,44,47,30,160,40,185,10,
```
+ 41,40,185,4.5,46.5,60,140,12,75,42,225,26,57, + 17,92,23.5,23.5,6,68), ncol=2, byrow=T)

[,1] [,2]
[1,] 7.0 47
[2,] 4.0 38
[3,] 20.0 96
[4,] 1.0 14
[5,] 10.0 48
[6,] 2.0 101
[7,] 12.0 161
[8,] 1.0 28
[9,] 1.0 19
[10,] 22.0 49
[11,] 25.0 162
[12,] 31.0 200
[13,] 9.0 39
[14,] 22.0 193
[15,] 0.5 46
[16,] 31.0 131
[17,] 4.0 75
[18,] 31.0 220
[19,] 7.0 55
[20,] 3.0 91
[21,] 14.5 26
[22,] 3.0 65
[23,] 25.0 54
[24,] 24.0 41
[25,] 37.0 95
[26,] 11.0 17
[27,] 26.0 49
[28,] 13.0 84
[29,] 38.0 170
[30,] 29.0 60
[31,] 9.0 20
[32,] 44.0 47
[33,] 30.0 160
[34,] 40.0 185
[35,] 10.0 41
[36,] 40.0 185
[37,] 4.5 46
[38,] 60.0 140
[39,] 12.0 75
[40,] 42.0 225
[41,] 26.0 57
[42,] 17.0 92
[43,] 23.5 24
[44,] 6.0 68

Note the problems in rows 15, 21, 37 and 43. They should read [0.5, 45.5],
[14.5, 21.5], etc... The matrix function seems to be rounding the second
column up to the next integer. Why would this occur? Can I do something to prevent this?

I would very much appreciate any comments.

Thanks,

Brant Inman
Mayo Clinic

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