spark 学习笔记 show()

 def show(numRows: Int): Unit = show(numRows, truncate = true)

  /**
   * Displays the top 20 rows of Dataset in a tabular form. Strings more than 20 characters
   * will be truncated, and all cells will be aligned right.
   *
   * @group action
   * @since 1.6.0
   */
  def show(): Unit = show(20)

  /**
   * Displays the top 20 rows of Dataset in a tabular form.
   *
   * @param truncate Whether truncate long strings. If true, strings more than 20 characters will
   *                 be truncated and all cells will be aligned right
   *
   * @group action
   * @since 1.6.0
   */
  def show(truncate: Boolean): Unit = show(20, truncate)

  /**
   * Displays the Dataset in a tabular form. For example:
   * {{{
   *   year  month AVG('Adj Close) MAX('Adj Close)
   *   1980  12    0.503218        0.595103
   *   1981  01    0.523289        0.570307
   *   1982  02    0.436504        0.475256
   *   1983  03    0.410516        0.442194
   *   1984  04    0.450090        0.483521
   * }}}
   * @param numRows Number of rows to show
   * @param truncate Whether truncate long strings. If true, strings more than 20 characters will
   *              be truncated and all cells will be aligned right
   *
   * @group action
   * @since 1.6.0
   */
  // scalastyle:off println
  def show(numRows: Int, truncate: Boolean): Unit = if (truncate) {
    println(showString(numRows, truncate = 20))
  } else {
    println(showString(numRows, truncate = 0))
  }

  /**
   * Displays the Dataset in a tabular form. For example:
   * {{{
   *   year  month AVG('Adj Close) MAX('Adj Close)
   *   1980  12    0.503218        0.595103
   *   1981  01    0.523289        0.570307
   *   1982  02    0.436504        0.475256
   *   1983  03    0.410516        0.442194
   *   1984  04    0.450090        0.483521
   * }}}
   *
   * @param numRows Number of rows to show
   * @param truncate If set to more than 0, truncates strings to `truncate` characters and
   *                    all cells will be aligned right.
   * @group action
   * @since 1.6.0
   */
  def show(numRows: Int, truncate: Int): Unit = show(numRows, truncate, vertical = false)

  /**
   * Displays the Dataset in a tabular form. For example:
   * {{{
   *   year  month AVG('Adj Close) MAX('Adj Close)
   *   1980  12    0.503218        0.595103
   *   1981  01    0.523289        0.570307
   *   1982  02    0.436504        0.475256
   *   1983  03    0.410516        0.442194
   *   1984  04    0.450090        0.483521
   * }}}
   *
   * If `vertical` enabled, this command prints output rows vertically (one line per column value)?
   *
   * {{{
   * -RECORD 0-------------------
   *  year            | 1980
   *  month           | 12
   *  AVG('Adj Close) | 0.503218
   *  AVG('Adj Close) | 0.595103
   * -RECORD 1-------------------
   *  year            | 1981
   *  month           | 01
   *  AVG('Adj Close) | 0.523289
   *  AVG('Adj Close) | 0.570307
   * -RECORD 2-------------------
   *  year            | 1982
   *  month           | 02
   *  AVG('Adj Close) | 0.436504
   *  AVG('Adj Close) | 0.475256
   * -RECORD 3-------------------
   *  year            | 1983
   *  month           | 03
   *  AVG('Adj Close) | 0.410516
   *  AVG('Adj Close) | 0.442194
   * -RECORD 4-------------------
   *  year            | 1984
   *  month           | 04
   *  AVG('Adj Close) | 0.450090
   *  AVG('Adj Close) | 0.483521
   * }}}
   *
   * @param numRows Number of rows to show
   * @param truncate If set to more than 0, truncates strings to `truncate` characters and
   *                    all cells will be aligned right.
   * @param vertical If set to true, prints output rows vertically (one line per column value).
   * @group action
   * @since 2.3.0
   */
  // scalastyle:off println
  def show(numRows: Int, truncate: Int, vertical: Boolean): Unit =
    println(showString(numRows, truncate, vertical))
  // scalastyle:on println

  /**
   * Returns a [[DataFrameNaFunctions]] for working with missing data.
   * {{{
   *   // Dropping rows containing any null values.
   *   ds.na.drop()
   * }}}
   *
   * @group untypedrel
   * @since 1.6.0
   */

函数重载

第一个参数：返回的行数

第二个参数：bool或者int类型，flase代表字段内容全部展示，true代表只展示20个字符，或者可以自动指定

第三个参数：是否垂直打印，默认为false

df.show()
#返回20行
df.show(30)
#返回30行
df.show(30,false)
#返回30行，且字段内容全部展示（默认展示20个字符）