Describe the bug In the example given here the function group_blocks_by_distance doesn't sort within row in the x direction. I came up with a simple fix to this as implemented below, and thought I would flag it for anyone else who runs into this issue.

To Reproduce Steps to reproduce the behavior:

What command or script did you run?


def group_blocks_by_distance(blocks, distance_th):

blocks = sorted(blocks, key = lambda x: x.coordinates[1])
distances = np.array([b2.coordinates[1] - b1.coordinates[3] for (b1, b2) in zip(blocks, blocks[1:])])

distances = np.append([0], distances)
block_group = (distances>distance_th).cumsum()

grouped_blocks = [lp.Layout([]) for i in range(max(block_group)+1)]
for i, block in zip(block_group, blocks):
    grouped_blocks[i].append(block)

return grouped_blocks

The changes that I implement here allow for within row sorting on the x axis, either from left to right or from right to left depending on the parameter passed.

left to right if x_direction = 0, right to left if x_direction = 1

def group_blocks_by_distance(blocks, distance_th, x_direction): blocks = sorted(blocks, key = lambda x: (x.coordinates[1])) distances = np.array([b2.coordinates[1] - b1.coordinates[3] for (b1, b2) in zip(blocks, blocks[1:])])

distances = np.append([0], distances)
block_group = (distances>distance_th).cumsum()
grouped_blocks = [[] for i in range(max(block_group)+1)]
for i, block in zip(block_group, blocks):
    grouped_blocks[i].append(block)
for i in range(len(grouped_blocks)):
    grouped_blocks[i] = sorted(grouped_blocks[i], 
                               key = lambda x: (x.coordinates[0]), 
                               reverse= x_direction)

grouped_sorted_blocks = [lp.Layout(grouped_blocks[i]) for i in range(max(block_group)+1)]

return grouped_sorted_blocks


**Environment**
I'm on Mac, using layoutparser version 0.2.0, working in a conda virtual environment. 

**Screenshots**
Lets say I have the following row. 
![image](https://user-images.githubusercontent.com/22862614/122645552-efda8e00-d0e8-11eb-836c-d0ffb6a68440.png)
The original function reads it as 
![image](https://user-images.githubusercontent.com/22862614/122645571-fcf77d00-d0e8-11eb-8a71-7fe9a81c8c6d.png)
My modification reads it as 
![image](https://user-images.githubusercontent.com/22862614/122645635-45af3600-d0e9-11eb-9bcd-0197ae11344d.png)

Layout-Parser / layout-parser

group_blocks_by_distance example addition #48

left to right if x_direction = 0, right to left if x_direction = 1