agenis - 8 months ago 53

R Question

I have some difficulties with propagation of missing values in the context of matrix multiplication.

My first matrix

`X`

`X=structure(c(16, 19, 28, 32, 30, 22, 16, 13, 8, 6, 5, 3, 5, 5, 6, 13, 7, 10, 4, 2, 1, 2, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 7, 8, 8, 7, 7, 6, 6, 5, 5, 4, 4, 4, -16, -17, -20, -31, -25, -25, -16, -12, -13, -15, -9, -7), .Dim = c(12L, 5L), .Dimnames = list(NULL, c("meter1", "meter2", "meter3", "meter4", "meter5")))`

#### meter1 meter2 meter3 meter4 meter5

#### [1,] 16 5 0 7 -16

#### [2,] 19 5 0 8 -17

#### ...

My second matrix

`Z`

`Z`

`(1)*Meter1 + (-1)*Meter2 + (1)*Meter5`

`Z=structure(c(1, -1, 0, 0, 1, 0, 1, 1, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0), .Dim = c(5L, 4L), .Dimnames = list(NULL, c("city1", "city2", "city3", "city4")))`

#### city1 city2 city3 city4

#### [1,] 1 0 0 0

#### [2,] -1 1 0 0

#### [3,] 0 1 0 0

#### [4,] 0 0 1 0

#### [5,] 1 0 0 0

So to calculate the net flow per city I just have to do a matrix multiplication:

`X %*% Z`

#### city1 city2 city3 city4

#### [1,] -5 5 7 0

#### [2,] -3 5 8 0

#### ...

My problem is that there are lots of

`X`

`NA`

`set.seed(3); for (i in 1:10) X[sample.int(nrow(X), 1), sample.int(ncol(X), 1)] <- NA`

When I do the matrix multiplication the

`NA`

`NA`

`NA`

`sum(is.na(cbind(X[, 1] - X[, 2] + X[, 5], X[, 2] + X[, 3], X[, 4], 0)))`

#### [1] 11

I would like to know if there is a way

`NA`

Thanks,

Answer

Yes, I am sure this is what you need:

```
library(Matrix)
ZZ <- Matrix(Z, sparse = TRUE)
X %*% ZZ
#12 x 4 Matrix of class "dgeMatrix"
# city1 city2 city3 city4
# [1,] -5 5 7 0
# [2,] NA NA NA 0
# [3,] NA 6 8 0
# [4,] -12 13 7 0
# [5,] NA NA 7 0
# [6,] -13 10 6 0
# [7,] -4 NA NA 0
# [8,] -1 2 NA 0
# [9,] -6 1 5 0
#[10,] -11 2 4 0
#[11,] NA NA 4 0
#[12,] -5 1 4 0
```

As you expected, there are only 11 `NA`

.

**Follow-up**

It throws an error when I try to convert the result to a data frame:

`data.frame(X %*% ZZ)`

. How can I do it?

Use `data.frame(as.matrix(X %*% ZZ))`

.

Source (Stackoverflow)