How to make a statement true for column 5-6?

I have a matrix

M= [1  50 60  70  50  40
    2 NaN 10  20  10  10
    3 NaN 20 NaN NaN NaN
    1 NaN 60  30  40  50
    2  10 20  10  20 NaN
    1  30 20  40 NaN  50
    2 NaN 50  50 1 NaN];

I want to check that, for each row, whether it is ture that the element in column 2 is NaN and the elements in column 5-6 are both non-NaN. I tried to code like this:

P=isnan(M(:,2))&isfinite(M(:,5:6))

P = 7×2 logical array
   0   0
   1   1
   0   0
   1   1
   0   0
   0   0
   1   0

However, the result is in 2 columns, column "NaN in column 2 and non-NaN in column 5" and column "NaN in column 2 and non-NaN in column 6".

Could anyone please tell me how to have the answer in 1 column?

I think this code works,

P=isnan(M(:,2))&isfinite(M(:,5))&isfinite(M(:,6))

P = 7×1 logical array
   0
   1
   0
   1
   0
   0
   0

but is there a better way to express "column 5-6" instead of making a isfinite statement for each column seperately?

Answer 1

[Voss]

'is there a better way to express "column 5-6"'

Yes.

You can use all(). Specifically, all(~isnan(__),2) where the 2 tells all() to operate over the columns (2nd dimension). ("All are non-NaN.")

Or you can use any(). Specifically, ~any(isnan(__),2). ("Not any are NaN.")

M = [1  50 60  70  50  40
    2 NaN 10  20  10  10
    3 NaN 20 NaN NaN NaN
    1 NaN 60  30  40  50
    2  10 20  10  20 NaN
    1  30 20  40 NaN  50
    2 NaN 50  50 1 NaN];

These three are equivalent:

P = isnan(M(:,2)) & ~isnan(M(:,5)) & ~isnan(M(:,6))

P = 7×1 logical array
   0
   1
   0
   1
   0
   0
   0

P = isnan(M(:,2)) & all(~isnan(M(:,[5 6])),2)

P = 7×1 logical array
   0
   1
   0
   1
   0
   0
   0

P = isnan(M(:,2)) & ~any(isnan(M(:,[5 6])),2)

P = 7×1 logical array
   0
   1
   0
   1
   0
   0
   0

Note that I'm using ~isnan() where you used isfinite(). The difference is how Inf and -Inf are treated.

~isnan(Inf)

ans = logical
   1

isfinite(Inf)

ans = logical
   0

And since the rules you describe talk about NaN vs non-NaN and say nothing about finte vs infinite, I think it makes sense to use isnan and ~isnan.

[Julia]

Thank you so much for guiding me through the logic behind this question! And thank you for pointing out the difference between ~isnan and isfinite.

[Voss]

You're welcome!