We’re going to change the previous solution to pull out the core dataset representing the raw data we’re interested in from the access log – records-from-access-log remains unchanged from before:

(defn access-log-to-dataset
  [filename]
  (col-names (to-dataset (records-from-access-log filename)) ["Date" "User"]))

The raw dataset retrieved from this call looks like this:

Now, we need to work out the number of unique users in a given time period. Like before, we’re going to use $rollup to group multiple records by minute, but we need to work out how to summarise the user column. To do this, we create a custom summarise function which calculates the number of unique users:

(defn num-unique-items
  [seq]
  (count (set seq)))

Then use that to modify the raw dataset and graph the resulting dataset:

(defn access-log-to-unique-user-dataset
  [access-log-dataset]
    ($rollup num-unique-items "User" "Date"
      (col-names (conj-cols ($map #(round-ms-down-to-nearest-min (as-millis %)) "Date" access-log-dataset) ($ "User" access-log-dataset)) ["Date" "Unique Users"])))

(defn concurrent-users-graph
  [dataset]
  (time-series-plot :Date :User
                             :x-label "Date"
                             :y-label "User"
                             :title "Users Per Min"
                             :data (access-log-to-unique-user-dataset dataset)))

(def access-log-dataset
  (access-log-to-dataset "/path/to/access.log"))

(save (concurrent-users-graph access-log-dataset) "unique-users.png")

You can see the full source code listing here.