# [R] Using lm with a matrix?

jonboym jonboym2 at yahoo.co.uk
Sat Jun 7 14:13:40 CEST 2008

```I'm trying to do a linear regression between the columns of matrices.  In
example below I want to regress column 1 of matrix xdat with column1 of ydat
and do a separate regression between the column 2s of each matrix.  But the
output I get seems to give correct slopes but incorrect intercepts and
another set of slopes with value NA.  How do I do this correctly?  I'm after
the slope and intercept of each columns regression

> xdat <- matrix(1:6,3,2)
> xdat
[,1] [,2]
[1,]    1    4
[2,]    2    5
[3,]    3    6
> ydat <- xdat
> ydat[,1] <- xdat[,1]*3 +2
> ydat
[,1] [,2]
[1,]    5    4
[2,]    8    5
[3,]   11    6
> ydat[,2] <- xdat[,2]*4 - 3
> ydat
[,1] [,2]
[1,]    5   13
[2,]    8   17
[3,]   11   21
> lrg <- lm(y~x)
> lrg <- lm(ydat~xdat)
> lrg

Call:
lm(formula = ydat ~ xdat)

Coefficients:
[,1]  [,2]
(Intercept)   2     9
xdat1         3     4
xdat2        NA    NA

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```