ARROW-11898: [Rust] Pretty print columns

Adds a way to also pretty-print a slice of columns, as a convenience to aviod creating a single-column record batch.

Closes #9650 from nevi-me/pretty-print-col

Authored-by: Neville Dipale <nevilledips@gmail.com>
Signed-off-by: Andrew Lamb <andrew@nerdnetworks.org>

Author: nevi-me

rust/arrow/src/util/pretty.rs

@@ -18,7 +18,7 @@
 //! Utilities for printing record batches. Note this module is not
 //! available unless `feature = "prettyprint"` is enabled.
 
-use crate::record_batch::RecordBatch;
+use crate::{array::ArrayRef, record_batch::RecordBatch};
 
 use prettytable::format;
 use prettytable::{Cell, Row, Table};
@@ -32,12 +32,23 @@ pub fn pretty_format_batches(results: &[RecordBatch]) -> Result<String> {
     Ok(create_table(results)?.to_string())
 }
 
+///! Create a visual representation of columns
+pub fn pretty_format_columns(col_name: &str, results: &[ArrayRef]) -> Result<String> {
+    Ok(create_column(col_name, results)?.to_string())
+}
+
 ///! Prints a visual representation of record batches to stdout
 pub fn print_batches(results: &[RecordBatch]) -> Result<()> {
     create_table(results)?.printstd();
     Ok(())
 }
 
+///! Prints a visual representation of a list of column to stdout
+pub fn print_columns(col_name: &str, results: &[ArrayRef]) -> Result<()> {
+    create_column(col_name, results)?.printstd();
+    Ok(())
+}
+
 ///! Convert a series of record batches into a table
 fn create_table(results: &[RecordBatch]) -> Result<Table> {
     let mut table = Table::new();
@@ -69,6 +80,28 @@ fn create_table(results: &[RecordBatch]) -> Result<Table> {
     Ok(table)
 }
 
+fn create_column(field: &str, columns: &[ArrayRef]) -> Result<Table> {
+    let mut table = Table::new();
+    table.set_format(*format::consts::FORMAT_NO_LINESEP_WITH_TITLE);
+
+    if columns.is_empty() {
+        return Ok(table);
+    }
+
+    let header = vec![Cell::new(field)];
+    table.set_titles(Row::new(header));
+
+    for col in columns {
+        for row in 0..col.len() {
+            let mut cells = Vec::new();
+            cells.push(Cell::new(&array_value_to_string(&col, row)?));
+            table.add_row(Row::new(cells));
+        }
+    }
+
+    Ok(table)
+}
+
 #[cfg(test)]
 mod tests {
     use crate::{
@@ -132,6 +165,32 @@ mod tests {
         Ok(())
     }
 
+    #[test]
+    fn test_pretty_format_columns() -> Result<()> {
+        let columns = vec![
+            Arc::new(array::StringArray::from(vec![
+                Some("a"),
+                Some("b"),
+                None,
+                Some("d"),
+            ])) as ArrayRef,
+            Arc::new(array::StringArray::from(vec![Some("e"), None, Some("g")])),
+        ];
+
+        let table = pretty_format_columns("a", &columns)?;
+
+        let expected = vec![
+            "+---+", "| a |", "+---+", "| a |", "| b |", "|   |", "| d |", "| e |",
+            "|   |", "| g |", "+---+",
+        ];
+
+        let actual: Vec<&str> = table.lines().collect();
+
+        assert_eq!(expected, actual, "Actual result:\n{}", table);
+
+        Ok(())
+    }
+
     #[test]
     fn test_pretty_format_null() {
         let schema = Arc::new(Schema::new(vec![