1. INTEGRATING
1.1. CONCATENATING
1.1.1. vertical
1.1.1.1. concept
1.1.1.1.1. check in R...
1.1.2. horizontal
1.1.2.1. concept
1.1.2.1.1. check in R
1.2. MERGING
1.2.1. Key
1.2.1.1. DFs to be merged must share common column values in one or several columns
1.2.1.1.1. DF location
1.2.1.1.2. DF key uniqueness
1.2.2. the Varieties of Merge
1.2.2.1. **Default result**: only matches when the same 'key' is present in both DFs
1.2.2.1.1. AKA: inner join
1.2.2.2. Keeping all rows from...
1.2.2.2.1. **LEFT (X)** DF
1.2.2.2.2. **RIGHT (Y)** DF
1.2.2.2.3. **BOTH- Left and Right (X and Y)** DFs
2. AGGREGATING
2.1. Data
2.1.1. Purpose
2.1.1.1. simplify
2.1.1.2. summarize
2.1.2. Elements
2.1.2.1. Grouping
2.1.2.1.1. Categorical / Discrete
2.1.2.2. Apply
2.1.2.2.1. Function
2.1.2.3. Input
2.1.2.3.1. Variable (individual?)
3. RESHAPING
3.1. Long to Wide
3.1.1. easier to compute stats for unit of analysis
3.2. Wide to Long
3.2.1. you avoid missing cells
3.2.2. easier for complex plots and some longitudinal methods
3.3. These processes help discover issues
3.3.1. key repetitions
3.3.2. key mistypying