# R: union of matrices every time a row is from one matrix with all rows in another matrix

I have 2 females ( `expmat`

and `mat`

). Let's say`expmat`

```
[1,] -1 -1 -1 -1 -1
[2,] 1 -1 -1 -1 -1
[3,] -1 1 -1 -1 -1
[4,] 1 1 -1 -1 -1
[5,] -1 -1 1 -1 -1
[6,] 1 -1 1 -1 -1
[7,] -1 1 1 -1 -1
[8,] 1 1 1 -1 -1
```

and `mat`

there is

```
[1,] -2 -2 -2 -2 -2
[2,] 2 -2 -2 -2 -2
[3,] -2 2 -2 -2 -2
[4,] 2 2 -2 -2 -2
[5,] -2 -2 2 -2 -2
[6,] 2 -2 2 -2 -2
[7,] -2 2 2 -2 -2
```

I would like to create a loop where in each loop I join one row from `expmat`

to all rows in the mat so that at the end 8 matrices are created, and in each matrix at first 5 columns are exactly the same (row from `expmat`

) and other columns change. since they come from the mat. For example, the first 2 matrices of the given example will look like

```
Matrix1
-1 -1 -1 -1 -1 -2 -2 -2 -2 -2
-1 -1 -1 -1 -1 2 -2 -2 -2 -2
-1 -1 -1 -1 -1 -2 2 -2 -2 -2
-1 -1 -1 -1 -1 2 2 -2 -2 -2
-1 -1 -1 -1 -1 -2 -2 2 -2 -2
-1 -1 -1 -1 -1 2 -2 2 -2 -2
-1 -1 -1 -1 -1 -2 2 2 -2 -2
Matrix 2
1 -1 -1 -1 -1 -2 -2 -2 -2 -2
1 -1 -1 -1 -1 2 -2 -2 -2 -2
1 -1 -1 -1 -1 -2 2 -2 -2 -2
1 -1 -1 -1 -1 2 2 -2 -2 -2
1 -1 -1 -1 -1 -2 -2 2 -2 -2
1 -1 -1 -1 -1 2 -2 2 -2 -2
1 -1 -1 -1 -1 -2 2 2 -2 -2
```

This is what I am doing:

```
for(row in 1:nrow(expmat)) {
for(row in 1:nrow(expmat)) {
val<-expmat[row,]
val<-as.matrix(val)
dshybrid=merge(t(val),mat, by=0, all=TRUE)
print(dshybrid)}
```

However, I get what I need instead

```
-1 -1 -1 -1 -1 -2 -2 -2 -2 -2
NA NA NA NA NA 2 -2 -2 -2 -2
NA NA NA NA NA -2 2 -2 -2 -2
NA NA NA NA NA 2 2 -2 -2 -2
NA NA NA NA NA -2 -2 2 -2 -2
NA NA NA NA NA 2 -2 2 -2 -2
NA NA NA NA NA -2 2 2 -2 -2
....
```

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This approach does the trick:

```
lapply(split(expmat, row(expmat)), function(u){
cbind(matrix(rep(u,nrow(mat)), ncol=ncol(mat), byrow=T), mat)
})
```

`split`

Will basically compile a list of strings `expmat`

, then for each row you duplicate it 7 times and concatenate with a matrix `mat`

. This will give you the 8 matrices you want.

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Adjust the loop for each line `expmat`

, `cbind`

by aiming it at `mat`

:

```
lapply(1:nrow(expmat), function(x) cbind(expmat[rep(x,nrow(mat)),],mat) )
```

`rep`

requires one line to `expmat`

repeat for each line `mat`

to which it is appended. For example, with a very simple example:

```
expmat <- matrix(1:4,nrow=2)
mat <- matrix(5:8,nrow=2)
lapply(1:nrow(expmat), function(x) cbind(expmat[rep(x,nrow(mat)),],mat) )
#[[1]]
# [,1] [,2] [,3] [,4]
#[1,] 1 3 5 7
#[2,] 1 3 6 8
#
#[[2]]
# [,1] [,2] [,3] [,4]
#[1,] 2 4 5 7
#[2,] 2 4 6 8
```

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