I have problem makin sub-materia (S) from matrix M.

To sub-materia i need to choose colums a,b &c and rows 20-120.

I tried like this, but it didn't work out:

```
S <- M [M $a & M $ b & M $ c & 20:120,,drop=FALSE $ M]
```

After that i should do a new sub-materia M1 from recently creates submateria M choosing sekond row.

This should go somelike:

M1 <- M [c(1, 3),]
but i dont know how to make it loop over and over again.

Here is a quick reminder about how to process select parts of matrices...

```
(am <- matrix(1:30,nrow=10,ncol=3))
colnames(am) <- letters[1:3]
#starting from this example matrix
am
#columns b & c
am[,c("b","c")]
#rows 3 to 7
am[3:7,]
#columns b & c & #rows 3 to 7
am[3:7,c("b","c")]
```

1 Like

Thank you, now i got the first part! I thought it way too complicated

Still haven't figure out how to choose evere second row.

every second row ? There are actually many ways to do this.. here is an explicit way

```
(even_numbers <-seq(from=2,
to=nrow(am),
by=2))
am[even_numbers,]
```

I'm sorry i mean that i should get every other row from one -> 1,3,5,7....n

Yes of course, silly me (I'm so tired that i consired even numbers as 2,4,6...)
But now i can go to sleep. Thank you for that!

system
Closed
December 17, 2020, 6:10pm
8
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