Rearrange data in a single column into multiple columns with Excel Power Query

It seems like this approach should work, but I don't know how to do the third step.

Column1  |  Column2
-------------------
  null   |    A
   a     |    2
   b     |    1
   c     |    6
  null   |    B
   a     |    5
   b     |    4
   c     |    3

Add conditional Column3 based off of Column1

Column1  |  Column2  |  Column3
-------------------------------
  null   |    A      |    0
   a     |    2      |   null
   b     |    1      |   null
   c     |    6      |   null
  null   |    B      |    0
   a     |    5      |   null
   b     |    4      |   null
   c     |    3      |   null

Here is the step I do not know how to do! In this simple example, there is only one change.

Column1  |  Column2  |  Column3
-------------------------------
  null   |    A      |    0
   a     |    2      |   null
   b     |    1      |   null
   c     |    6      |   null
  null   |    B      |    1
   a     |    5      |   null
   b     |    4      |   null
   c     |    3      |   null

Fill Column3 down

Column1  |  Column2  |  Column3
-------------------------------
  null   |    A      |    0
   a     |    2      |    0
   b     |    1      |    0
   c     |    6      |    0
  null   |    B      |    1
   a     |    5      |    1
   b     |    4      |    1
   c     |    3      |    1

Pivot

Column1  |    0      |    1
-------------------------------
  null   |    A      |   null
  null   |   null    |    B
   a     |    2      |   null
   a     |   null    |    5
   b     |    1      |   null
   b     |   null    |    4
   c     |    6      |   null
   c     |   null    |    3

Fill Upward on (Column) 1, Filter null on (Column) 0

Column1  |    0      |    1
-------------------------------
  null   |    A      |    B
   a     |    2      |    5
   b     |    1      |    4
   c     |    6      |    3

Here is the way I solved this after a search. Note that this is not ideal because it only works for a fixed size file. This could be parameterized, but there is likely a way to make it work for a variable sized file without needing the sizes entered as parameters. Also, I scrambled the data a bit to more closely resemble the actual problem.

This is a simplified rendition of my .yaml file. I read this in as text without delimiters.

 A:
   a: 2
   b: 1
   c: 6
 B:
   a: 5
   b: 4
   c: 3

By using the Find & Replace (I used four steps)

,A
a,2
b,1
c,6
,B
a,5
b,4
c,3

Split Column by Delimiter (a comma here)

Column1  |  Column2
-------------------
  null   |    A
   a     |    2
   b     |    1
   c     |    6
  null   |    B
   a     |    5
   b     |    4
   c     |    3

Added Index and Inserted Modulo 4 column(operates on Column3 to create Column4)

Column1  |  Column2  |  Column3  |  Column4
-------------------------------------------
  null   |    A      |     0     |    0
   a     |    2      |     1     |    1
   b     |    1      |     2     |    2
   c     |    6      |     3     |    3
  null   |    B      |     4     |    0
   a     |    5      |     5     |    1
   b     |    4      |     6     |    2
   c     |    3      |     7     |    3

Sorted Rows by Column4, added another index, and added a modulo 2 column.

Column1  |  Column2  |  Column3  |  Column4  |  Column5  |  Column6
-------------------------------------------------------------------
  null   |    A      |     0     |     0     |     0     |    0
  null   |    B      |     4     |     0     |     1     |    1
   a     |    2      |     1     |     1     |     2     |    0
   a     |    5      |     5     |     1     |     3     |    1
   b     |    1      |     2     |     2     |     4     |    0
   b     |    4      |     6     |     2     |     5     |    1
   c     |    6      |     3     |     3     |     6     |    0
   c     |    3      |     7     |     3     |     7     |    1

Sort on Column6 to get groupings of rows that will go into a single column, with the column number in Column6

Column1  |  Column2  |  Column3  |  Column4  |  Column5  |  Column6
-------------------------------------------------------------------
  null   |    A      |     0     |     0     |     0     |    0
   a     |    2      |     1     |     1     |     2     |    0
   b     |    1      |     2     |     2     |     4     |    0
   c     |    6      |     3     |     3     |     6     |    0
  null   |    B      |     4     |     0     |     1     |    1
   a     |    5      |     5     |     1     |     3     |    1
   b     |    4      |     6     |     2     |     5     |    1
   c     |    3      |     7     |     3     |     7     |    1

Pivot on Column6 with Values coming from Column2

Column1  |  Column3  |  Column4  |  Column5  |    0    |    1
-----------------------------------------------------------------
  null   |     0     |     0     |     0     |    A    |   null
  null   |     4     |     0     |     1     |   null  |    B
   a     |     1     |     1     |     2     |    2    |   null
   a     |     5     |     1     |     3     |   null  |    5
   b     |     2     |     2     |     4     |    1    |   null
   b     |     6     |     2     |     5     |   null  |    4
   c     |     3     |     3     |     6     |    6    |   null   
   c     |     7     |     3     |     7     |   null  |    3

Fill up (Column) 1

Column1  |  Column3  |  Column4  |  Column5  |    0    |    1
-----------------------------------------------------------------
  null   |     0     |     0     |     0     |    A    |    B
  null   |     4     |     0     |     1     |   null  |    B
   a     |     1     |     1     |     2     |    2    |    5
   a     |     5     |     1     |     3     |   null  |    5
   b     |     2     |     2     |     4     |    1    |    4
   b     |     6     |     2     |     5     |   null  |    4
   c     |     3     |     3     |     6     |    6    |    3   
   c     |     7     |     3     |     7     |   null  |    3

Filter (Column) 0 on null and remove Column3, Column4, and Column5 to get the final result

Column1  |    0    |    1
-----------------------------
  null   |    A    |    B
   a     |    2    |    5
   b     |    1    |    4
   c     |    6    |    3