Counting nulls

[Dicken]

Hi, 
    counting null values,    i have; 

= let alist = 
{1,2,2,"a",null, null, 2,"a",3,2,null, "a"} 
in 
List.Count( alist) - List.NonNullCount( alist)


or 

= let alist = 
{1,2,2,"a",null, null, 2,"a",3,2,null, "a"} 
in 
List.Count( List.Select( alist, (x)=> 
 Value.Is(x, type null)) )

woud anyone like to suggest differerent / better way  ?  

[Parchitect · Accepted solution]

Hi @Dicken,

For pure null values, I would keep your first approach. It is probably the cleanest and easiest to read:

let
    alist = {1,2,2,"a",null, null, 2,"a",3,2,null, "a"}
in
    List.Count(alist) - List.NonNullCount(alist)

List.NonNullCount is built to count non-null items, so total count minus non-null count gives the null count.

[slorin]

You don't need List.Accumulate, just List.Transform

List.Transform( alist , each Number.From(_ = null))

[Dicken]

I know, I just liked it. 

[Dicken]

a take on the accumulate version, so not to count but show where null;

= let alist = {"a",1,null, null,"a",3,"b"} 
, t = "a" 
in   List.Accumulate( alist, {}  , (s,c)=> 
  s & { Number.From( c = null ) } )

[slorin · Accepted solution]

List.Accumulate(alist, 0, (i,x) => i + Number.From(x=null))

List.Sum(List.Transform( alist, each Number.From(_=null)))

[Dicken]

penny dropped,  coerecing  true / false to 1 ,0   

[Dicken]

really like that, only now i have to look into why it works as 
Number.From(_  = null) 
Number.From(_ ) = null)
are not the same 

[AlienSx]

let
    fx = (x, y) => if List.Count(x) = 0 then y else @ fx(List.Skip(x), y + Number.From(x{0} = null))
in
    fx({1, 2, 2, "a", null, null, 2, "a", 3, 2, null, "a"}, 0)

[Dicken]

just to add recgarding the count , remove nul,   i did say count nulls. 

[jgeddes]

My bad. I removed my answer as a solution. You could do this...

let 
    alist = 
    {1,2,2,"a",null, null, 2,"a",3,2,null, "a"} 
in 
    List.Count( alist ) - List.Count( List.RemoveNulls( alist ))

[slorin]

Hi,

List.Count(List.PositionOf(alist, null, Occurrence.All))

Stéphane

[Dicken]

Thanks to all responses,  always nice to see what I had not thought of.

[jgeddes]

This should work too...

let 
    alist = 
    {1,2,2,"a",null, null, 2,"a",3,2,null, "a"} 
in 
    List.Count( List.RemoveNulls( alist ))

[Parchitect · Accepted solution]

Hi @Dicken,

For pure null values, I would keep your first approach. It is probably the cleanest and easiest to read:

let
    alist = {1,2,2,"a",null, null, 2,"a",3,2,null, "a"}
in
    List.Count(alist) - List.NonNullCount(alist)

List.NonNullCount is built to count non-null items, so total count minus non-null count gives the null count.