将函数应用于R中数据框的列中的每个单元格

Question

EDIT Thanks to @user5249203 for pointing out that geocoding is best done with ggmaps' geocode call. Watch out for NA's though.

I am struggling with the apply family in R.

I am using a function which takes in a string and returns longitude and latitude

> gGeoCode("Philadelphia, PA") [1] 39.95258 -75.16522

I have a simple dataframe which has the names of all 52 states:

dput(state_lat_long)
structure(
  list(State = structure(
    c(
      32L, 28L, 43L, 5L, 23L, 34L,
      30L, 13L, 14L, 38L, 22L, 25L, 15L, 20L, 24L, 40L, 46L, 21L, 9L,
      18L, 48L, 10L, 7L, 4L, 3L, 31L, 35L, 37L, 49L, 44L, 12L, 6L,
      17L, 36L, 11L, 39L, 42L, 8L, 47L, 33L, 16L, 1L, 29L, 27L, 26L,
      19L, 41L, 50L, 2L, 45L
    ), .Label = c(
      "alabama", "alaska", "arizona",
      "arkansas", "california", "colorado", "connecticut", "delaware",
      "florida", "georgia", "hawaii", "idaho", "illinois", "indiana",
      "iowa", "kansas", "kentucky", "louisiana", "maine", "maryland",
      "massachusetts", "michigan", "minnesota", "mississippi", "missouri",
      "montana", "nebraska", "nevada", "new hampshire", "new jersey",
      "new mexico", "new york", "north carolina", "north dakota", "ohio",
      "oklahoma", "oregon", "pennsylvania", "rhode island", "south carolina",
      "south dakota", "tennessee", "texas", "utah", "vermont", "virginia",
      "washington", "west virginia", "wisconsin", "wyoming"
    ), class = "factor"
  )), .Names = "State", row.names = c(NA,-50L), class = "data.frame"
)

To practice my apply skills, I simply want to apply gGeoCode to each cell in the only column of the state_lat_long dataframe.

Couldn't be much simpler.

Then what is the problem with this?

> View(apply(state_lat_long, function(x) gGeoCode(x)))

When I run this, I get:

Error in View : argument "FUN" is missing, with no default  

which I don't understand, because FUN is not missing.

So, let's try sapply . It's supposed to be simple, right?

But what is wrong with this?

View(sapply(state_lat_long$State, function(x) gGeoCode(x)))

When I run this, I get 2 rows with 50 columns, packed with NA s. I can't make sense of it.

Next, I tried

View(apply(state_lat_long, 2, function(x) gGeoCode(x)))  

and I got

     State
  40.71278
 -74.00594  

Again, this makes no sense!

What am I doing wrong? Thanks.

Answer 1

Is this how your data frame is ?

df = data.frame(State = c(
    32L, 28L, 43L, 5L, 23L, 34L,
    30L, 13L, 14L, 38L, 22L, 25L, 15L, 20L, 24L, 40L, 46L, 21L, 9L,
    18L, 48L, 10L, 7L, 4L, 3L, 31L, 35L, 37L, 49L, 44L, 12L, 6L,
    17L, 36L, 11L, 39L, 42L, 8L, 47L, 33L, 16L, 1L, 29L, 27L, 26L,
    19L, 41L, 50L, 2L, 45L
  ), Label = c(
    "alabama", "alaska", "arizona",
    "arkansas", "california", "colorado", "connecticut", "delaware",
    "florida", "georgia", "hawaii", "idaho", "illinois", "indiana",
    "iowa", "kansas", "kentucky", "louisiana", "maine", "maryland",
    "massachusetts", "michigan", "minnesota", "mississippi", "missouri",
    "montana", "nebraska", "nevada", "new hampshire", "new jersey",
    "new mexico", "new york", "north carolina", "north dakota", "ohio",
    "oklahoma", "oregon", "pennsylvania", "rhode island", "south carolina",
    "south dakota", "tennessee", "texas", "utah", "vermont", "virginia",
    "washington", "west virginia", "wisconsin", "wyoming"
  ))

head(df)
  State      Label
1    32    alabama
2    28     alaska
3    43    arizona
4     5   arkansas
5    23 california
6    34   colorado

apply(df, 1, function(x) gGeoCode(x))

Alternatively,

mapply(FUN = gGeoCode, df$Label, SIMPLIFY = T)

Note: Some states still throws NA . Re-run of the code fetches the missing coordinates. But, I expect it to work more efficiently if we know your input format/ dataframe construction. Also, it is important to make sure the arguments you pass are what the gGeoCode expects.

Answer 2

I realise this question was primarily about *apply , but, if you were only after geocodes an easier option would be to use a vectorised function, such as ggmap::geocode

state_lat_long <- structure(
    list(State = structure(
    c(
      32L, 28L, 43L, 5L, 23L, 34L,
      30L, 13L, 14L, 38L, 22L, 25L, 15L, 20L, 24L, 40L, 46L, 21L, 9L,
      18L, 48L, 10L, 7L, 4L, 3L, 31L, 35L, 37L, 49L, 44L, 12L, 6L,
      17L, 36L, 11L, 39L, 42L, 8L, 47L, 33L, 16L, 1L, 29L, 27L, 26L,
      19L, 41L, 50L, 2L, 45L
    ), .Label = c(
      "alabama", "alaska", "arizona",
      "arkansas", "california", "colorado", "connecticut", "delaware",
      "florida", "georgia", "hawaii", "idaho", "illinois", "indiana",
      "iowa", "kansas", "kentucky", "louisiana", "maine", "maryland",
      "massachusetts", "michigan", "minnesota", "mississippi", "missouri",
      "montana", "nebraska", "nevada", "new hampshire", "new jersey",
      "new mexico", "new york", "north carolina", "north dakota", "ohio",
      "oklahoma", "oregon", "pennsylvania", "rhode island", "south carolina",
      "south dakota", "tennessee", "texas", "utah", "vermont", "virginia",
      "washington", "west virginia", "wisconsin", "wyoming"
    ), class = "factor"
  )), .Names = "State", row.names = c(NA,-50L), class = "data.frame"
)

library(ggmap)

## to make sure we're using the correct geocode function I call it with 'ggmap::geocode'
ggmap::geocode(as.character(state_lat_long$State))
...
#           lon      lat
# 1   -74.00594 40.71278
# 2  -116.41939 38.80261
# 3   -99.90181 31.96860
# 4  -119.41793 36.77826
# 5   -94.68590 46.72955
# 6  -101.00201 47.55149