Parsing JSON in Excel VBA

Question

I have the same issue as in Excel VBA: Parsed JSON Object Loop but cannot find any solution. My JSON has nested objects so suggested solution like VBJSON and vba-json do not

Answer 1

To parse JSON in VBA without adding a huge library to your workbook project, I created the following solution. It's extremely fast and stores all of the keys and values in a dictionary for easy access:

Function ParseJSON(json$, Optional key$ = "obj") As Object
    p = 1
    token = Tokenize(json)
    Set dic = CreateObject("Scripting.Dictionary")
    If token(p) = "{" Then ParseObj key Else ParseArr key
    Set ParseJSON = dic
End Function

Function ParseObj(key$)
    Do: p = p + 1
        Select Case token(p)
            Case "]"
            Case "[":  ParseArr key
            Case "{"
                       If token(p + 1) = "}" Then
                           p = p + 1
                           dic.Add key, "null"
                       Else
                           ParseObj key
                       End If
            
            Case "}":  key = ReducePath(key): Exit Do
            Case ":":  key = key & "." & token(p - 1)
            Case ",":  key = ReducePath(key)
            Case Else: If token(p + 1) <> ":" Then dic.Add key, token(p)
        End Select
    Loop
End Function

Function ParseArr(key$)
    Dim e&
    Do: p = p + 1
        Select Case token(p)
            Case "}"
            Case "{":  ParseObj key & ArrayID(e)
            Case "[":  ParseArr key
            Case "]":  Exit Do
            Case ":":  key = key & ArrayID(e)
            Case ",":  e = e + 1
            Case Else: dic.Add key & ArrayID(e), token(p)
        End Select
    Loop
End Function

The code above does use a few helper functions, but the above is the meat of it.

The strategy used here is to employ a recursive tokenizer. I found it interesting enough to write an article about this solution on Medium. It explains the details.

Here is the full (yet surprisingly short) code listing, including all of the helper functions:

'-------------------------------------------------------------------
' VBA JSON Parser
'-------------------------------------------------------------------
Option Explicit
Private p&, token, dic
Function ParseJSON(json$, Optional key$ = "obj") As Object
    p = 1
    token = Tokenize(json)
    Set dic = CreateObject("Scripting.Dictionary")
    If token(p) = "{" Then ParseObj key Else ParseArr key
    Set ParseJSON = dic
End Function
Function ParseObj(key$)
    Do: p = p + 1
        Select Case token(p)
            Case "]"
            Case "[":  ParseArr key
            Case "{"
                       If token(p + 1) = "}" Then
                           p = p + 1
                           dic.Add key, "null"
                       Else
                           ParseObj key
                       End If
            
            Case "}":  key = ReducePath(key): Exit Do
            Case ":":  key = key & "." & token(p - 1)
            Case ",":  key = ReducePath(key)
            Case Else: If token(p + 1) <> ":" Then dic.Add key, token(p)
        End Select
    Loop
End Function
Function ParseArr(key$)
    Dim e&
    Do: p = p + 1
        Select Case token(p)
            Case "}"
            Case "{":  ParseObj key & ArrayID(e)
            Case "[":  ParseArr key
            Case "]":  Exit Do
            Case ":":  key = key & ArrayID(e)
            Case ",":  e = e + 1
            Case Else: dic.Add key & ArrayID(e), token(p)
        End Select
    Loop
End Function
'-------------------------------------------------------------------
' Support Functions
'-------------------------------------------------------------------
Function Tokenize(s$)
    Const Pattern = """(([^""\\]|\\.)*)""|[+\-]?(?:0|[1-9]\d*)(?:\.\d*)?(?:[eE][+\-]?\d+)?|\w+|[^\s""']+?"
    Tokenize = RExtract(s, Pattern, True)
End Function
Function RExtract(s$, Pattern, Optional bGroup1Bias As Boolean, Optional bGlobal As Boolean = True)
  Dim c&, m, n, v
  With CreateObject("vbscript.regexp")
    .Global = bGlobal
    .MultiLine = False
    .IgnoreCase = True
    .Pattern = Pattern
    If .TEST(s) Then
      Set m = .Execute(s)
      ReDim v(1 To m.Count)
      For Each n In m
        c = c + 1
        v(c) = n.value
        If bGroup1Bias Then If Len(n.submatches(0)) Or n.value = """""" Then v(c) = n.submatches(0)
      Next
    End If
  End With
  RExtract = v
End Function
Function ArrayID$(e)
    ArrayID = "(" & e & ")"
End Function
Function ReducePath$(key$)
    If InStr(key, ".") Then ReducePath = Left(key, InStrRev(key, ".") - 1)
End Function
Function ListPaths(dic)
    Dim s$, v
    For Each v In dic
        s = s & v & " --> " & dic(v) & vbLf
    Next
    Debug.Print s
End Function
Function GetFilteredValues(dic, match)
    Dim c&, i&, v, w
    v = dic.keys
    ReDim w(1 To dic.Count)
    For i = 0 To UBound(v)
        If v(i) Like match Then
            c = c + 1
            w(c) = dic(v(i))
        End If
    Next
    ReDim Preserve w(1 To c)
    GetFilteredValues = w
End Function
Function GetFilteredTable(dic, cols)
    Dim c&, i&, j&, v, w, z
    v = dic.keys
    z = GetFilteredValues(dic, cols(0))
    ReDim w(1 To UBound(z), 1 To UBound(cols) + 1)
    For j = 1 To UBound(cols) + 1
         z = GetFilteredValues(dic, cols(j - 1))
         For i = 1 To UBound(z)
            w(i, j) = z(i)
         Next
    Next
    GetFilteredTable = w
End Function
Function OpenTextFile$(f)
    With CreateObject("ADODB.Stream")
        .Charset = "utf-8"
        .Open
        .LoadFromFile f
        OpenTextFile = .ReadText
    End With
End Function