I am regularly running into a problem where I can't seem to figure out how
maintain correct data order when selecting data out of a dataframe. The
below code shows an example of trying to pull data from a dataframe using
ordered zip codes. My problem is returning the pulled data in the correct
order. This is a very simple example, but it illustrates a regular problem
that I am running into.
In the past, I have used fairly complicated solutions to pull this off.
There has got to be a more simple and straightforward method ... probably
some function that I missed in all my googling.
Thanks in advance for anybody's help figuring this out.
~Markus
### Function Definitions ###
# FUNCTION #1 (returns wrong order)
getLatitude1 = function(myzips) {
# load libraries and data
library(zipcode)
data(zipcode)
# get latitude values
mylats = zipcode[zipcode$zip %in% myzips, "latitude"] #problem is that
this code does not maintain order
# return data
return(mylats)
}
# FUNCTION #2 (also returns wrong order)
getLatitude2 = function(myzips) {
# load libraries and data
library(zipcode)
data(zipcode)
# convert myzips to DF
myzips = as.data.frame(as.character(myzips))
# merge in zipcode data based on zip
results = merge(myzips, zipcode[,c("zip", "latitude")], by.x =
"as.character(myzips)", by.y="zip", all.x=TRUE)
# return data
return(results$latitude)
}
### Code ###
# specify a set of zip codes
myzips = c("74432", "72537", "06026", "01085", "65793")
# create a DF
myzips.df = data.frame(zip=myzips, latitude=NA, longitude=NA)
# look at data to determine what should be returned and in what order
library(zipcode)
data(zipcode)
zipcode[zipcode$zip %in% myzips,]
# test function #1 (function definition below)
myzips.df$latitude = getLatitude1(myzips.df$zip) #returns wrong order
# test function #2 (function definition below)
myzips.df$latitude = getLatitude2(myzips.df$zip) #also returns wrong order
# need "myzips %in% zipcode$zip" to return array/df indices rather than
logical
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