Messages from Usenet group comp.lang.idl-pvwave, compiled by Paulo Penteado
An interesting feature of the colon operator caught me by surprise. Using the two examples from the IDL help page www.harrisgeospatial.com/docs/Creating_Arrays.html IDL> Help, [[1:5], [6:10], 11, [11:16], 17, 18, 19, 20, [21:30]] <Expression> INT = Array[31] IDL> Help, [[10:19], [20:29], [30:39]] <Expression> INT = Array[10, 3] The first example results in an Nx1 array while the second example results in an Nx3 array despite the similarity in appearance. The latter is consistent with non-colon-operator array concatenation, the former is not. It gets more complicated when I want to combine an Nx1 with an Mx1 array to get an Lx1 array. IDL> Help, [ 0:10:0.1, 0:10:0.5 ] ^ % Illegal array creation syntax. IDL> Help, [ [0:10:0.1], [0:10:0.5] ] % Unable to concatenate variables because the dimensions do not agree: <FLOAT Array[21]>. % Execution halted at: $MAIN$ To get the Lx1 array, I have to do one of the following IDL> Help, Reform( [ [Transpose([0:10:0.1])], [Transpose([0:10:0.5])] ] ) <Expression> FLOAT = Array[122] IDL> Help, [ [0:10:0.1], !Null, [0:10:0.5] ] <Expression> FLOAT = Array[122]