Getting data out

Read data from Nominal into a timetable, a file on disk, or a SQL result table.

Finding a dataset

c.assets and c.datasets return every asset or dataset whose name contains the text you pass, ignoring case, as a table that includes each match’s RID.

c.assets("<search text>")
ds = c.datasetByRid(c.datasets("<search text>").Rid(1));
ds.channels()                              % the channels in the dataset

Always pass search text. With no argument, c.assets() and c.datasets() return every asset or dataset in the workspace in one call.

Reading a channel

fetch reads one numeric channel into a timetable.

t1 = datetime("now", TimeZone="UTC");
t0 = t1 - hours(2);

tt = ds.fetch("<channel>", t0, t1);
plot(tt.Time, tt.(1))

To plot a wide window, have Nominal reduce it to roughly a given number of points:

tt = ds.fetch("<channel>", t0, t1, Buckets=2000);

Each of those points is the mean of its bucket, so short spikes are smoothed out. Fetch without Buckets when you need them.

synchronize lines up channels on one time axis:

ch1  = ds.fetch("<channel 1>", t0, t1);
ch2  = ds.fetch("<channel 2>", t0, t1);
both = synchronize(ch1, ch2);

Through an asset or a run

a.fetch and r.fetch read a channel from one of their data sources, with that source’s tag filter and time offset applied. r.fetch reads from the run’s start to its end.

tt = a.fetch("<channel>", t0, t1);         % from the data source called "default"
tt = r.fetch("<channel>", RefName="<ref name>");

A run’s data in a .mat file

export writes a time window to a file in one request. A run shows its asset’s data sources, so get the dataset from the asset.

r  = c.runByRid("<run rid>");
a  = c.assetByRid(r.AssetRids(1));
ds = c.datasetByRid(a.datasources().Rid(1));

% export takes numeric channels only. A string channel fails the whole export.
ch      = ds.channels();
numeric = ch.Name(ismember(ch.DataType, ["double" "int" "uint"]))';
ds.export("run.mat", numeric, r.StartTime, r.EndTime);

Pass Format="csv" or Format="arrow" for the other formats. ds.exportUrl returns a time-limited download link instead of a file.

SQL

c.query runs a query and returns a table.

t = c.query("SELECT ts, channel, value FROM points_double " + ...
            "WHERE dataset_rid = '" + ds.Rid + "' ORDER BY ts LIMIT 100");
t.ts = nominal.fromNanos(t.ts);            % timestamps come back as int64 nanoseconds

Queries on telemetry tables must filter on dataset_rid. The SQL reference lists the tables and their columns.

Results over 1 GiB need c.queryExportUrl(sql), which returns a download link to a CSV file.