replace na in column in data frame r code example

Example 1: replace any NA in a data frame in r

a = data.frame(a=c(NA,1,2,NA), b=c(1,1,2,NA),c=c(NA,NA,2,NA))
for (i in 1:3){
  a[which(is.na(a[,i])),i] = 0
}

Example 2: replace na in a column with values from another df

library(dplyr)

df1 %>% inner_join(df2, by= "ID") %>%
  mutate(Count = coalesce(Count.x, Count.y)) %>%
  select(ID, Count)

#   ID Count
# 1 11   345
# 2 22   456
# 3 33   786
# 4 44   765
# 5 55   890
# 6 66   888
# 7 77   654