Let's look now at a dataset from another general election, this time from Russia in 2011. Russia is a much larger country, and its election data is much larger too. We'll be loading two large Excel files into the memory, which may exceed your default JVM heap size.

To expand the amount of memory available to Incanter, we can adjust the JVM settings in the project's profile.clj. The a vector of configuration flags for the JVM can be provided with the key :jvm-opts. Here we're using Java's Xmx flag to increase the heap size to 1GB. This should be more than enough.

  :jvm-opts ["-Xmx1G"]

Russia's data is available in two data files. Fortunately the columns are the same in each, so they can be concatenated together end-to-end. Incanter's function i/conj-rows exists for precisely this purpose:

(defmethod load-data :ru [_]
  (i/conj-rows (-> (io/resource "Russia2011_1of2.xls")
                   (str)
                   (xls/read-xls))
               (-> (io/resource "Russia2011_2of2.xls")
                   (str)
                   (xls/read-xls))))

In the preceding code, we define a third implementation of the load-data multimethod to load and combine both Russia files.

Let's see what the Russia data column names are:

(defn ex-1-29 []
  (-> (load-data :ru)
      (i/col-names)))

;; ["Code for district"
;; "Number of the polling district (unique to state, not overall)"
;; "Name of district" "Number of voters included in voters list"
;; "The number of ballots received by the precinct election
;; commission" ...]

The column names in the Russia dataset are very descriptive, but perhaps longer than we want to type out. Also, it would be convenient if columns that represent the same attributes as we've already seen in the UK election data (the victor's share and turnout for example) were labeled the same in both datasets. Let's rename them accordingly.

Along with a dataset, the i/rename-cols function expects to receive a map whose keys are the current column names with values corresponding to the desired new column name. If we combine this with the i/add-derived-column data we have already seen, we arrive at the following:

(defmethod load-data :ru-victors [_]
  (->> (load-data :ru)
       (i/rename-cols
        {"Number of voters included in voters list" :electorate
         "Number of valid ballots" :valid-ballots
         "United Russia" :victors})
       (i/add-derived-column :victors-share
                             [:victors :valid-ballots] i/safe-div)
       (i/add-derived-column :turnout
                             [:valid-ballots :electorate] /)))

The i/safe-div function is identical to / but will protect against division by zero. Rather than raising an exception, it returns the value Infinity, which will be ignored by Incanter's statistical and charting functions.