[FIXED] numpy 2D array matching

Issue

I'm trying to find the starting coordinates of a small 2D array (b) in a large numpy 2D array (a), I've written this method but it's too complicated and slow, does anyone have a better idea?

a=[[5 4 5 9 3 4 6 2 5 3]
   [8 3 5 4 3 4 5 8 4 4]
   [5 7 8 5 2 3 3 6 8 8]
   [4 5 6 2 6 5 6 7 9 3]
   [3 6 8 2 8 7 3 8 8 8]]

b=[[2 3 3]
   [6 5 6]]

def screen_match(img1,img2):
    match_1=list(img1.T[1])
    img_len=len(match_1)
    # img2=img2.tolist()
    is_match=False
    position=[]
    for i in range(img2.shape[1]):
        img2_col=img2[:, i].tolist()
        for j in range(len(img2_col)):
            img2_cut=img2_col[j:j+img_len]
            if match_1== img2_cut:
                inner_col=i+1
                for m in range(2,img1.shape[1]):
                    inner_img1 = list(img1.T[m])
                    for n in range(i+1,img2.shape[1]):
                        inner_img2_col = img2[:, inner_col].tolist()
                        inner_img2_cut = inner_img2_col[j:j + img_len]
                        if inner_img1==inner_img2_cut:
                            is_match=True
                            break
                        else:
                            is_match=False
                            break
                    inner_col += 1
                    if not is_match:break
                if is_match:
                    position=[i,j]
                    break
            if is_match:break
        if is_match:
            print(position)
            break
    return position

Solution

You can use fancy indexing to reduce the number of nested loops

# Rename variables for clarity
array = a
kernel = b

array_H, array_W = array.shape
kernel_H, kernel_W = kernel.shape
def search_array():
    for x in range(0,array_W-kernel_W):
        for y in range(0,array_H-kernel_H):
           array_subsection = array[y:y+kernel_H, x:x+kernel_W]
           if array_subection == kernel:
               print(f"kernel was found at x={x}, y={y}.")
               return
    print(f"kernel was not found in array.")
search_array()

Answered By - Michael Sohnen