Q:

Remove Duplicates by Unique Value in another Column

I have a dataframe that looks like this: 
  COLA       COLB     COLC
    A         nb       1
    A         nc       0.8
    A         bc       0.7
    A         nb       0.7  <------------
    B         nb       1
    B         nc       0.3  <------------
    B         nc       0.8
    B         aa       0.9

I want to remove the duplicates in COLB by COLA unique ID and keep the maximum value of that duplicate from COLC. 
So I want the final result to look like this ( pointed to the rows I want to delete in the previous table): 
  COLA       COLB     COLC
    A         nb       1
    A         nc       0.8
    A         bc       0.7
    B         nb       1
    B         nc       0.8
    B         aa       0.9

A:

We can use dplyr.  After arrangeing the 'COLA", and descendingly the 'COLC', we group by 'COLA', 'COLB' and get the first row with slice.
library(dplyr)
df1 %>%
   arrange(COLA, desc(COLC)) %>% 
   group_by(COLA, COLB) %>% 
   slice(1L) 

