[Gretl-devel] Re: Datatypes of json items

On Sun, 23 Jun 2019, Artur Tarassow wrote: > Am 23.06.19 um 15:06 schrieb Allin Cottrell: >> On Mon, 17 Jun 2019, Allin Cottrell wrote: >> >>> On Sat, 15 Jun 2019, Artur Tarassow wrote: >>> >>>> Dear all, >>>> >>>> I hope you had a successful gretl conference in Naples! >>>> >>>> I am currently working with json files again. Using latest git >>>> version of >>>> gretl on Ubuntu linux (even though the behavior also occurs for older >>>> versions), I've found that some of the json-elements grabbed are >>>> not of the >>>> expected datatype. See the the following example and the file >>>> attached: >>>> >>>> >>>> <hansl> >>>> string PATH2JSON = "/home/at/tmp/"                    # set your path >>>> string jsonfile = sprintf("%s/ex_json_num_vector.json", PATH2JSON) >>>> string jread = readfile("@jsonfile") better: readfile(jsonfile)

>>>> bundle B = jsongetb(jread) >>>> b = B.JSON >>>> >>>> # Evaluate type of elements >>>> #----------------------------------------------------- >>>> # Item         Expected        Is >>>> # v1        string                null >>>> # v2        string array       string array >>>> # v3        scalar               scalar >>>> # v4        matrix              string array >>>> >>>> loop i=1..nelem(b) -q >>>>      string str = "v$i" >>>>      eval b["@str"] >>>>      eval typestr(typeof(b["@str"])) >>>>      print "" >>>> endloop >>>> </hansl> >>>> >>>> Is there a rational reason for this behavior? >>> Not really. It seems that typeof() is not reaching inside bundles to >>> find the type of their contents. That should be made to happen. >> Ah, that comment was not quite right: the failure of typeof() to reach >> inside bundles (and arrays) was specific to the case of string >> objects. That's now fixed in git; snapshots will follow. > > Thanks for the fix, Allin. However, why is a numeric vector (element > v4) treated as a string array even though it comprises numeric values > only? Is there any way to import it is a matrix datatype or some way > to transform it to such a datatype using gretl? We don't know the type of elements in a JSON array, they could be anything. So the safest thing is to store them as strings.

But of course there's a way to convert from strings to numerical values (assuming that makes sense) in gretl. Suppose that bundle b holds an element v4 which is a suitable array: <hansl> n = nelem(b.v4) matrix m = zeros(1, n) loop i=1..n -q   m[i] = atof(b.v4[i]) endloop m </hansl>