Using a table as a variable in a function

Question

I have a bunch of arrays and need to extract specific rows and columns of these that obey certain criteria. So for one table I'd do like this

func[x_]=Cases[table,{n_,__}/;a[x]<n<b[x]]

where b[x] and a[x] are numeric functions of a real number that I defined earlier. How can I do this so that func takes also a table as an argument? I've tried

func[table_?MatrixQ,x_]
func[table_?(MatrixQ[#,NumericQ]&),x_]

but they give me the same error

Array::argbu : Array called with 1 argument; between 2 and 4 arguments are expected

If it helps, the tables have only 2 columns (but the number of rows varies)

Answer 1

I believe you've just made a syntax error by leaving out && between the two inequality operators. If I understand your question, you should have functions defined as follows:

ClearAll[a, b, func];
a[x_Real] :=(* example calc *)-1*x;
b[x_Real] :=(* example calc *)x;
func[table_?(MatrixQ[#, NumericQ] &), x_] := 
    Cases[table, {n_, __} /; a[x] < n && b[x] > n];

...with an example in this case of a simple filtering operation on a matrix shown as follows:

First, let's create some data. This creates a real-valued matrix:

temp = Table[RandomReal[{-1, 1}], {i, 1, 5}, {j, 1, 5}];

To work with the same data, here's what I see:

temp = {{-0.19773, -0.403283, -0.203482, 
0.560051, -0.662339}, {-0.229652, -0.382093, -0.369309, 0.576484, 
0.566491}, {0.30776, 0.471342, 0.556337, 0.997326, 
0.749479}, {0.951397, 0.256563, 
0.740539, -0.9422, -0.552236}, {0.937068, 0.903586, -0.0219966, 
0.917632, 0.0494045}};

Now call func on the temp variable with some real value in place of x as follows:

func[temp, .3]

...which returns

{{-0.19773, -0.403283, -0.203482, 
0.560051, -0.662339}, {-0.229652, -0.382093, -0.369309, 0.576484, 
0.566491}}

You can see that func "filtered" the rows using the functions a and b (I'm just using your function names here for comparability sake) as well as the pattern variable n.