Coalesce columns in spark dataframe

Question

I did an algorithm and I got a lot of columns with the name logic and number suffix, I need to do coalesce but I don't know how to apply coalesce with different amount of columns.

Example:

|id|logic_01|logic_02|logic_03|
|1 |  null  |a       |null    |  
|2 |  null  |b       |null    |   
|3 |   c    | null   |null    |   
|4 |  null  | null   |d       |

Response:

|id|logic|
|1 |  a  |  
|2 |  b  |   
|3 |  c  |   
|4 |  d  | 

Another example:

|id|logic_01|logic_02|logic_03|logic_04|
|1 |  null  |a       |null    |null    |  
|2 |  null  | null   |null    |b       |   
|3 |   c    | null   |null    |null    |    
|4 |  null  | null   |d       |null    |

Response:

|id|logic|
|1 |  a  |  
|2 |  b  |   
|3 |  c  |   
|4 |  d  | 

Thanks for your help.

Answer 1

First find all columns that you want to use in the coalesce:

val cols = df.columns.filter(_.startsWith("logic")).map(col(_))

Then perform the actual coalesce:

df.select($"id", coalesce(cols: _*).as("logic"))