In[]:=
Dataset[{<|"a"->1,"b"->"x","c"->{1},"e"->f[],"d"->1|>,<|"a"->2,"b"->"y","c"->{2,3},​​"e"->g[],"d"->2|>,<|"a"->3,"b"->"z","c"->{3},"e"->h[],"d"->0|>,​​<|"a"->4,"b"->"x","c"->{4,5},"e"->f[],"d"->1|>,<|"a"->5,"b"->"y","c"->{5,6,7},​​"e"->g[],"d"->2|>,<|"a"->6,"b"->"z","c"->{},"e"->h[],"d"->0|>,​​<|"a"->7,"b"->"z","c"->{8,9},"e"->f[],"d"->1|>,<|"a"->8,"b"->"z","c"->{10,11,12},​​"e"->h[],"d"->2|>},TypeSystem`Vector[TypeSystem`Struct[{"a","b","c","e","d"},​​{TypeSystem`Atom[Integer],TypeSystem`Atom[TypeSystem`Enumeration["x","y","z"]],​​TypeSystem`Vector[TypeSystem`Atom[Integer],TypeSystem`AnyLength],TypeSystem`AnyType,​​TypeSystem`Atom[Integer]}],8],<|"ID"->173083105899894|>]
Out[]=
a
b
c
e
d
1
x
{1}
f[]
1
2
y
{2,3}
g[]
2
3
z
{3}
h[]
0
4
x
{4,5}
f[]
1
5
y
{5,6,7}
g[]
2
6
z
{}
h[]
0
7
z
{8,9}
f[]
1
8
z
{10,11,12}
h[]
2
In[]:=
dataset[Select[#b"x"&],{"a","e"}]​​dataset[Select[#b!="x"&],{"a","e"}]
Out[]=
a
e
1
f[]
4
f[]
Out[]=
a
e
2
g[]
3
h[]
5
g[]
6
h[]
7
f[]
8
h[]
In[]:=
dataset[Select[Head[#e]f&],{"a","e"}]​​dataset[Select[Head[#e]≠f&],{"a","e"}]
Out[]=
a
e
1
f[]
4
f[]
7
f[]
Out[]=