library("tidyr")
library("dplyr")
## 
## Attaching package: 'dplyr'
## The following objects are masked from 'package:stats':
## 
##     filter, lag
## The following objects are masked from 'package:base':
## 
##     intersect, setdiff, setequal, union
df <- dplyr::data_frame(
  year = c(2015, NA, NA, NA,2017),
  count = c(1, NA, 2, NA,NA)
)
df 
## # A tibble: 5 x 2
##    year count
##   <dbl> <dbl>
## 1  2015     1
## 2    NA    NA
## 3    NA     2
## 4    NA    NA
## 5  2017    NA

fill and replace_na

fill(df ,year, count)
## # A tibble: 5 x 2
##    year count
##   <dbl> <dbl>
## 1  2015     1
## 2  2015     1
## 3  2015     2
## 4  2015     2
## 5  2017     2
replace_na(df, list(year=2016,count=10))
## # A tibble: 5 x 2
##    year count
##   <dbl> <dbl>
## 1  2015     1
## 2  2016    10
## 3  2016     2
## 4  2016    10
## 5  2017    10

fill all NA cell

df %>% replace(is.na(.),'Missing')
## # A tibble: 5 x 2
##      year   count
##     <chr>   <chr>
## 1    2015       1
## 2 Missing Missing
## 3 Missing       2
## 4 Missing Missing
## 5    2017 Missing

expend missing

df <- dplyr::data_frame(
  year = c(2015, NA, 2016, NA,2017),
  month = c(1, NA, 2, NA,3),
  count =c(1,2,3,4,5)
)
complete(df,year,month)%>%
replace(is.na(.),0)
## # A tibble: 9 x 3
##    year month count
##   <dbl> <dbl> <dbl>
## 1  2015     1     1
## 2  2015     2     0
## 3  2015     3     0
## 4  2016     1     0
## 5  2016     2     3
## 6  2016     3     0
## 7  2017     1     0
## 8  2017     2     0
## 9  2017     3     5

fill empty string

df <- dplyr::data_frame(
year = c(2015, '', '', '',2017),
count = c(1, '', 2, '',''))
df%>%
mutate(year=ifelse(year=="",'Unknow',year), count=ifelse(count=="",'0',count))
## # A tibble: 5 x 2
##     year count
##    <chr> <chr>
## 1   2015     1
## 2 Unknow     0
## 3 Unknow     2
## 4 Unknow     0
## 5   2017     0

split cell into row

df <- dplyr::data_frame(x = 1:2, y = c("1,2", "3,4,5,6,7"))
df%>%
mutate(y = strsplit(y, ","))%>%
unnest()
## # A tibble: 7 x 2
##       x     y
##   <int> <chr>
## 1     1     1
## 2     1     2
## 3     2     3
## 4     2     4
## 5     2     5
## 6     2     6
## 7     2     7