1. Appending/Concatenating
1.1. vertical
1.1.1. concept
1.1.1.1. Conditions
1.1.1.1.1. All DFs share the same column names.
1.1.1.1.2. All the DFs columns are in the same location.
1.1.1.2. check
1.1.1.2.1. All the DFs columns have the same data types.
1.1.1.2.2. Missing data created
1.2. horizontal
1.2.1. concept
1.2.1.1. check
1.2.1.1.1. row index or names in result
1.2.1.1.2. reset index in result
1.2.1.1.3. Missing data created
1.2.1.2. condition: same row names
2. Merging
2.1. Key
2.1.1. DFs to be merged must share common column values in one or several columns
2.1.1.1. DF location
2.1.1.1.1. Left or X
2.1.1.1.2. Right or Y
2.1.1.2. DF uniqueness
2.1.1.2.1. no duplicates
2.1.1.2.2. you may need to combine columns in some cases
2.2. the Varieties of Merge
2.2.1. **Default result**: only matches when the same 'key' is present in both DFs
2.2.1.1. AKA: inner join
2.2.2. Keeping all rows from...
2.2.2.1. **LEFT (X)** DF
2.2.2.1.1. AKA: left join
2.2.2.2. **RIGHT (Y)** DF
2.2.2.2.1. AKA: right join
2.2.2.3. **BOTH- Left and Right (X and Y)** DFs
2.2.2.3.1. AKA: outer join
2.3. Fuzzy Merge
2.3.1. Algorithm to match similar keys