arrays - Java 8 Lambda to convert Number[][] to double[][] -

number[][] intarray = new integer[][]{ {1, 2, 3}, {4, 5, 6}, {7, 8, 9} }; double[][] doublearray = arrays.stream(intarray)                             .foreach(parray -> arrays.stream(parray)                                                 .maptodouble(d ->d.doublevalue())                                                 .toarray())                             .toarray(); 

i want convert number[][] double[][]. above lambda not work, outer toarray not compile.

arrays.stream(intarray) : returns stream of integer[]
foreach : every integer[], creating stream of integers, converting each integer double , returning double[].
the each creates double[] , thought outer toarray return array of double[]
how can work?

here's how it:

double[][] doublearray = arrays.stream(intarray)                                .map(arr -> stream.of(arr).maptodouble(number::doublevalue).toarray())                                .toarray(double[][]::new); 

this can decomposed follows:

first use arrays.stream create stream<number[]>. each number[], create stream<number>, , use maptodouble doublestream , toarray() double[] array.

the final toarray call transforms stream<double[]> double[][] array.