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Apply a function to each partition of a SparkDataFrame.

Usage

dapply(x, func, schema)

# S4 method for class 'SparkDataFrame,function,characterOrstructType'
dapply(x, func, schema)

Arguments

x

A SparkDataFrame

func

A function to be applied to each partition of the SparkDataFrame. func should have only one parameter, to which a R data.frame corresponds to each partition will be passed. The output of func should be a R data.frame.

schema

The schema of the resulting SparkDataFrame after the function is applied. It must match the output of func. Since Spark 2.3, the DDL-formatted string is also supported for the schema.

Note

dapply since 2.0.0

Examples

if (FALSE) { # \dontrun{
  df <- createDataFrame(iris)
  df1 <- dapply(df, function(x) { x }, schema(df))
  collect(df1)

  # filter and add a column
  df <- createDataFrame(
          list(list(1L, 1, "1"), list(2L, 2, "2"), list(3L, 3, "3")),
          c("a", "b", "c"))
  schema <- structType(structField("a", "integer"), structField("b", "double"),
                     structField("c", "string"), structField("d", "integer"))
  df1 <- dapply(
           df,
           function(x) {
             y <- x[x[1] > 1, ]
             y <- cbind(y, y[1] + 1L)
           },
           schema)

  # The schema also can be specified in a DDL-formatted string.
  schema <- "a INT, d DOUBLE, c STRING, d INT"
  df1 <- dapply(
           df,
           function(x) {
             y <- x[x[1] > 1, ]
             y <- cbind(y, y[1] + 1L)
           },
           schema)

  collect(df1)
  # the result
  #       a b c d
  #     1 2 2 2 3
  #     2 3 3 3 4
} # }