Renaming of Column names in Model.matrix

Question

Can any one help me in renaming of column names of model.matix?

I have been trying to rename my columns:

colnames(model.matrix(reg))[1] <- c("Intercept")

but I am getting error message:

could not find function "model.matrix<-"

Here is the model.matrix object:

model.matrix.default(reg)
   xxXB(Intercept) xxXBproductPageViews xxXBqty_order xxXBLag.sales
2         1.782842             2352.032      1.804487      303.0831
4         1.782842             1569.158      1.799786      369.0831
5         1.782842             2541.884      1.806206      434.7506
6         1.782842             2932.289      1.811827      414.7104
7         1.782842             2670.780      1.798207      360.4423
8         1.782842             2694.579      1.793033      291.9571
9         1.782842             5435.900      1.791143      325.7292
10        1.782842            10727.969      1.807148      602.7453
11        1.782842            12711.044      1.826717     1130.3189
12        1.782842            10774.425      1.808426     1694.6620
13        1.782842             8597.127      1.789496     1611.1204
14        1.782842             7647.235      1.789358     1161.2223
15        1.782842             5538.071      1.798733      979.3913
16        1.782842             4240.954      1.798549      813.5173
17        1.782842             3890.973      1.787179      668.3082
18        1.782842             4086.364      1.816897      563.1715
19        1.782842             4878.903      1.815232      552.4128
20        1.782842             3999.407      1.787328      612.4691
21        1.782842             3349.887      1.875233      526.7774
22        1.782842             5394.895      1.891263      599.2761
23        1.782842             4682.374      1.817970     1290.7023
24        1.782842             3346.345      1.805635     1057.0534
25        1.782842             3106.214      1.839484      638.3726
26        1.782842             4559.091      1.878944      611.1822
attr(,"assign")
[1] 1 1 1 1

The above matrix is matrix of lm equation called reg. Now how can I change column names of model.matrix?

Please provide a [reproducible example](http://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example). — Thomas, Aug 16 '13 at 11:18
xxXB(Intercept), xxXBproductPageViews, xxXBqty_order, xxXBLag.sales are the column names but i want to remove xxXB from all column names. — kapil, Aug 16 '13 at 11:27
Isn't that `model.matrix.default(reg)` and not model.matrix.(reg) in `colnames...` — Metrics, Aug 16 '13 at 11:37

Thomas · Answer 1 · 2013-08-16T11:56:27.600

10

You need to store the model.matrix result first then rename its columns.

mm <- model.matrix(reg)
colnames(mm)[1] <- c("Intercept")

More generally you could could use gsub to replace the "xxXB" part from all the names with:

colnames(mm) <- gsub("xxXB","",colnames(mm))

An alternative approach would involve the following:

`colnames<-`(model.matrix(reg),1:4)

where 1:4 is a vector of replacement names of the appropriate length. I think the first solution is easier (and more flexible), though.

edited Aug 16 '13 at 11:56

answered Aug 16 '13 at 11:44

Thomas

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Thanks ..but what went wrong in colnames(model.matrix(reg))[1] <- c("Intercept") ?? why do we need to assign a variable ?? – kapil Aug 16 '13 at 15:30
@kapil I'm not 100% sure, but I think it has to do with the fact that R doesn't interpret the contents of the call as a matrix. Maybe lazy evaluation or something about these particular methods, but this occurs with all `*names` functions. – Thomas Aug 16 '13 at 17:55
@Thomas your first option was very helpful for me, thks. But I have many matrix, how can I rename only colnames "Zinc" and "Magnesium" by "Zn" and "Mg"?. I tried it, but doesn't work: Eg. `colnames(mm)[c("Zinc", "Magnesium")] <- c("Zn", "Mg")` – Darwin PC Aug 17 '15 at 13:51
@DarwinPC Can you post that as a new question? – Thomas Aug 17 '15 at 15:29
@Thomas I have posted a new question [Here](http://stackoverflow.com/questions/32075485/how-to-rename-a-specific-colname-by-name-in-a-matrix-rather-than-numerical-inde) – Darwin PC Aug 18 '15 at 14:39

score -1 · Answer 2 · edited Mar 23 '17 at 03:07

-1

Is model.matrix a function? Are you wanting to give the result from sending 'reg' to model.matrix() a new name? The error means that the type does not have a <- method. Look in R help for [<-.factor for more info.

If this is the case though model.matrix (which you spelled model.matix) does not have columns, its a function, you want to change the names of its return.

Try this

model.matrix <- function(x) {
      matrix(runif(4), nrow = 2, ncol = 2,
            dimnames = list(c("r1", "r2"), c("C1", "C2")))
    }

And what you are doing

colnames(model.matrix(1))[1] <- 'a'

will not work but you can do the following

x <- model.matrix(1)
colnames(x)[1] <- 'a'

I'm just giving an argument of 1 because I am not sure what you 'reg' is.

edited Mar 23 '17 at 03:07

luchonacho

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answered Aug 16 '13 at 11:53

darrelkj

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`model.matrix` is a function in the **stats** package (loaded by default)...so redefining it as you suggest is probably not helpful. – Thomas Aug 16 '13 at 12:05
I am only defining it so that it acts like the function you are using, I can now give it a constant and get the same return type. I am not recommending you to redefine it. It was a stand in to make the problem reproducible, otherwise I need to create reg to run. The part that is answering the question is after that. – darrelkj Aug 16 '13 at 13:18

Renaming of Column names in Model.matrix

2 Answers2