The namespace clojure.pprint has some useful function to pretty print different data structures. The function print-table is particularly useful for printing a collection of maps, where each map represents a row in the table, and the keys of the maps represent the column headers. The print-table function accepts the collection as argument and prints the table to the console (or any writer that is bound to the *out* var). We can also pass a vector with the keys we want to include in the table. Only the keys we specify are in the output. The order of the keys in the vector we pass as argument is also preserved in the generated output.

In the following example code we use the print-table function to print some conference data that is stored in a vector of maps. We use the function with-out-str to capture the output of print-table so we can compare it with our expected result. In the example we first call print-table with the full conferences vector, and then we call it again with a vector of specific keys we want to include in the output.

(ns mrhaki.sample.print-table
  (:require [clojure.pprint :refer [print-table]]
            [clojure.test :refer [is]])
  (:import [java.io StringWriter]))

;; Vector with maps representing conference information.
(def conferences [{:name "Javaland" :location "Nürburgring" :country "Germany"}
                  {:name "JFall" :location "Ede" :country "The Netherlands"}
                  {:name "Full Stack Conference" :location "Nieuwegein" :country "The Netherlands"}])

;; Using print-table we get a nicely formatted table with all
;; rows from our conferences vector.
;; Each key name is a column header.
;; We use with-out-str function to capture the output
;; of the print-table function as String value.
(is (= "
|                 :name |   :location |        :country |
|-----------------------+-------------+-----------------|
|              Javaland | Nürburgring |         Germany |
|                 JFall |         Ede | The Netherlands |
| Full Stack Conference |  Nieuwegein | The Netherlands |
" (with-out-str (print-table conferences))))

;; Using print-table with a vector of keys we get a nicely formatted table
;; with all rows from our conferences vector.
;; But now the columns are only the keys we specified.
;; The order of the keys is also the order of the columns.
;; We use with-out-str function to capture the output
;; of the print-table function as String value.
(is (= "
|        :country |                 :name |
|-----------------+-----------------------|
|         Germany |              Javaland |
| The Netherlands |                 JFall |
| The Netherlands | Full Stack Conference |
" (with-out-str (print-table [:country :name] conferences))))

Written with Clojure 1.11.2.

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