R ifelse（）计算条件并返回匹配项

Question

I have a dataframe

countryname <- c("Viet Nam", "Viet Nam", "Viet Nam", "Viet Nam", "Viet Nam")
year <- c(1974, 1975, 1976, 1977,1978)

df <- data.frame(countryname, year)

that is in a long country by year format.

I would like to create a function that can standardize countrynames conditional upon the year of the observation. I created a function that is able to pull from a data frame cnames and standardize names but this is only useful for cross-sections and if country names do not vary over time.

country <- c("Vietnam, North", "Vietnam, N.", "Vietnam North", "Viet Nam", "Democratic Republic Of Vietnam")
standardize <- c("Vietnam, Democratic Republic of", "Vietnam, Democratic Republic of", "Vietnam, Democratic Republic of", "Vietnam, Democratic Republic of", "Vietnam, Democratic Republic of")
panel <- c("Vietnam", "Vietnam","Vietnam","Vietnam","Vietnam")
time <- c(1976,1976,1976,1976,1976)

cnames <- data.frame(country, standardize, panel, time)

The function to standardize is

country_name <- function(x) {
   return(cnames[match(x,cnames$country),]$standardize)
}

However, as you can see this doesn't account for any variation of country names over time. I've tried a number of different things and the closest I've come is this function.

country_panel <- function(x, y) {

  ifelse(cnames$time < y, 
    return(cnames[match(x, cnames$country),]$panel),
    return(cnames[match(x, cnames$country),]$standardize)
  )
}

I use a dplyr chain to pull in the data frame and then use mutate to create a new variable that ideally that captures the difference in names for countries.

d1 <- df %>%
    mutate(new_name = country_panel(countryname, year))

The problem that I'm finding is that the function only evaluates y in the country_panel function as a single object not as a vector. If I input an integer that is greater or less than cnames$time it evaluates correctly but passes the value for every row.

How can I have this function evaluate each cnames$country and cnames$time relationship to df$year and return the correct cnames$panel or cnames$standardize ?

Thank you for any help.

Answer 1

d1
#   countryname year                        new_name
# 1    Viet Nam 1974 Vietnam, Democratic Republic of
# 2    Viet Nam 1975 Vietnam, Democratic Republic of
# 3    Viet Nam 1976 Vietnam, Democratic Republic of
# 4    Viet Nam 1977                         Vietnam
# 5    Viet Nam 1978                         Vietnam

All you need to do is make sure your data frames are set to stringsAsFactors=F when you define them, ie ( df <- data.frame(countryname, year, stringsAsFactors=F) ). And take out the return command:

country_panel <- function(x, y) {
  ifelse(cnames$time < y, 
    cnames[match(x, cnames$country),]$panel,
    cnames[match(x, cnames$country),]$standardize
  )
}

The reasoning behind it is that return stops the function in its tracks once it's called. So your data frame is being populated by a single value output. That's why they were all the same.

Answer 2

You could join the tables based on year and country name:

left_join(df, cnames, by = c("countryname" = "country", "year" = "time"))

  countryname year                     standardize   panel
1    Viet Nam 1974                            <NA>    <NA>
2    Viet Nam 1975                            <NA>    <NA>
3    Viet Nam 1976 Vietnam, Democratic Republic of Vietnam
4    Viet Nam 1977                            <NA>    <NA>
5    Viet Nam 1978                            <NA>    <NA>