Replace NA with minimum Group Value R

Question

I'm struggeling with transforming my data and would appreciate some help

year	name	start
2010	Emma	1998
2011	Emma	1998
2012	Emma	1998
2009	John	na
2010	John	na
2012	John	na
2007	Louis	na
2012	Louis	na

the aim is to replace all NAs with the minimum value in year for every name group so the data looks like this

year	name	start
2010	Emma	1998
2011	Emma	1998
2012	Emma	1998
2009	John	2009
2010	John	2009
2012	John	2009
2007	Louis	2007
2012	Louis	2007

Note: either all start values of one name group are NAs or none

I tried to use

mydf %>%   group_by(name) %>%   mutate(start= ifelse(is.na(start), min(year, na.rm = T), start))

but got this error

x `start` must return compatible vectors across groups

There are a lot of similar problems here. Some people here used the ave function or worked with data.table which both doesnt seem to fit my problem

My base function must be sth like

df$A <- ifelse(is.na(df$A), df$B, df$A)

however I cant seem to properly combine it with the min() and group by() function.

Thank you for any help

Answer 1

We can use na.aggregate

library(dplyr)
library(zoo)
dat %>%
   group_by(name) %>%
   mutate(start = na.aggregate(na_if(start, "na"), FUN = min))