How to identify and remove errors in a list

Question

After some searching, I did not find a solution to the following problem, which in my thinking should have some very easy/efficient solution.

I'm looking at a list of images (faces), that I want to conform via FindFaces

faces = 
  ConformImages[HistogramTransform @ ImageTrim[#, FindFaces[#][1]]]& /@ images, 
    ColorSpace -> "Grayscale"]

So far this works like a charm and can also be found here: $\quad \quad $https://reference.wolfram.com/language/example/GenderClassification.html

PROBLEM: The problem is that FindFaces is unable to detect some images and thus creates an error. This error is carried forward into the results list.

GOAL: Essentially I want to simply drop the error from the list. I also need to extract the position of those images to drop corresponding values from a secondary variable.

As the initial problem is not reproducible, here my idea as a very simplified example:

results = Table[1/i, {i, -5, 5}]
results[[6]]
posDrop = 6
resultsClean = Delete[results, posDrop]

The 6th value of the list returns the error message "ComplexInfinity". To somehow extract the position (i.e. 6) would suffice, but I'm looking for a solution that does not require me to know the specific error message or, for the image problem, finding non-numeric entries.

Answer 1

You can use Check to return a particular value if an error is raised.

(* Here I return the string 'Error' which I can use to find the position of the errors. *)
test[x_] := Check[1/x, "Error"]; 
range = Range[-1,1,1];
ans = test/@range;(*Division by zero will raise a warning.*)
errPos = Position[ans,"Error"];
ans = Delete[ans,errPos];
range = Delete[range,errPos];

Edit: Check actually checks for all printed out messages. If you know you get a particular type of failure from your function, you can specify the message you want Check to respond to. In the case of dividing by zero you'd add Power::infy as the third argument, etc.