pd2hts - Read and write Pandas objects from/to Hydrognomon timeseries files

Requirements

Python 3, Pandas

Reference

pd2hts contains the following functions:

• read(f, start_date=None, end_date=None) reads filelike object f that contains a time series in text format, and returns a pandas DataFrame with date index, value, and flags. There must be no newline translation in f (open it with open(..., newline='\n'). If start_date and/or end_date are specified, it skips rows outside the range.

• read_file(f) reads filelike object f that contains a time series in file format, and returns a pandas DataFrame which also has attributes unit, title, comment, time_zone, time_step, timestamp_rounding, timestamp_offset, interval_type, variable, precision and location. For the meaning of these attributes, see section "File format" below. All these attributes are informational; they aren't otherwise taken into account in the pandas object.

  In particular, time_step and the other time-step-related attributes don't necessarily mean that the pandas object will have a related frequency. In fact, raw time series may be irregular but actually have a time step. For example, a ten-minute time series might end in :10, :20, etc., but at some point there might be an irregularity and it could continue with :31, :41, etc. Strictly speaking, such a time series has an irregular step. However, when stored in a database, specifying that its time step is ten minutes (because that's what it is, ten minutes with irregularities) can help people who browse or search the database contents.

  The location attribute is a dictionary that has items abscissa, ordinate, srid, altitude, and asrid.

• write(pd, f) writes pandas DataFrame pd, which should be a time series with value and flags, to filelike object f, in text format. In accordance with the :ref:`text format specification <textformat>`, time series are written using the CR-LF sequence to terminate lines. In order to produce fully compliant files, care should be taken that f, or any subsequent operations on f, do not perform text translation; otherwise, it may result in lines being terminated with CR-CR-LF. If f is a file, it should have been opened in binary mode.

• write_file(pd, f, version=4) is like write() but uses file format. If pd has any of the extra attributes mentioned in read_file(), these are written to the file.

Formats

There are two formats: the text format is generic text format, without metadata; the file format is like the text format, but additionally contains headers with metadata.

Text format

The text format for a time series is us-ascii, one line per record, like this:

2006-12-23 18:34,18.2,RANGE

The three fields are comma-separated and must always exist. In the date field, the time may be missing. The character that separates the date from the time may be either a space or a lower case t, or a capital T (this module produces text format using a space as date separator, but can read text format that uses t or T). The second field always uses a dot as the decimal separator and may be empty. The third field is usually empty but may contain a list of space-separated flags. The line separator should be the CR-LF sequence used in MS-DOS and Windows systems. Code that produces text format should always use CR-LF to end lines, but code that reads text format should be able to also read lines that end in LF only, as well as CR-CR-LF (for reasons explained in the write() function above).

In order to improve performance in file writes, the maximum length of each time series record line is limited to 255 characters.

Flags should be encoded in ASCII; there must be no characters with code greater than 127.

File format

The file format is like this:

Version=2
Title=My timeseries
Unit=°C

2006-12-23 18:34,18.2,RANGE
2006-12-23 18:44,18.3,

In other words, the file format consists of a header that specifies parameters in the form Parameter=Value, followed by a blank line, followed by the timeseries in text format. The same conventions for line terminators apply here as for the text format. The encoding of the header section is UTF-8.

Client and server software should recognize UTF-8 files with or without UTF-8 BOM (Byte Order Mark) in the begining of file. Writes may or may not include the BOM, according OS. (Usually Windows software attaches the BOM at the beginning of the file).

Parameter names are case insensitive. There may be white space on either side of the equal sign, which is ignored. Trailing white space on the line is also ignored. A second equal sign is considered to be part of the value. The value cannot contain a newline, but there is a way to have multi-lined parameters explained in the Comment parameter below. All parameters except Version are optional: either the value can be blank or the entire Parameter=Value can be missing; the only exception is the Comment parameter.

The parameters available are:

Version

There are four versions:

• Version 1 files are long obsolete. They did not have a header section.
• Version 2 files must have Version=2 as the first line of the file. All other parameters are optional. The file may not contain unrecognized parameters; software reading files with unrecognized parameters may raise an error.
• Version 3 files do not have the Version parameter. At least one of the other parameters must be present. Unrecognized parameters are ignored when reading. The deprecated parameter names Nominal_offset and Actual_offset are used instead of the newer ones Timestamp_rounding and Timestamp_offset.
• Version 4 files are the same as Version 3, except for the names of the parameters Timestamp_rounding and Timestamp_offset.

Unit

A symbol for the measurement unit, like °C or mm.

Count

The number of records in the time series. If present, it need not be exact; it can be an estimate. Its primary purpose is to enable progress indicators in software that takes time to read large time series files. In order to determine the actual number of records, the records need to be counted.

Title

A title for the time series.

Comment

A multiline comment for the time series. Multiline comments are stored by specifying multiple adjacent Comment parameters, like this:

Comment=This timeseries is extremely important
Comment=because the comment that describes it
Comment=spans five lines.
Comment=
Comment=These five lines form two paragraphs.

The Comment parameter is the only parameter where a blank value is significant and indicates an empty line, as can be seen in the example above.

Timezone

The time zone of the timestamps, in the format :samp:`{XXX} (UTC{+HHmm})`, where XXX is a time zone name and +HHmm is the offset from UTC. Examples are EET (UTC+0200) and VST (UTC-0430).

Time_step

A comma-separated pair of integers; the number of minutes and months in the time step (one of the two mut be zero). If missing, the time series is without time step.

Timestamp_rounding

A comma-separated pair of integers indicating the number of minutes and months that must be added to a round timestamp to get to the nominal timestamp. For example, if an hourly time series has timestamps that end in :13, such as 01:13, 02:13, etc., then its rounding is 13 minutes, 0 months, i.e., (13, 0). Monthly time series normally have a nominal timestamp of (0, 0), the timestamps usually being of the form 2008-02-01 00:00, meaning "February 2008" and usually rendered by application software as "Feb 2008" or "2008-02". Annual timestamps have a nominal timestamp which normally has 0 minutes, but may have nonzero months; for example, a common rounding in Greece is 9 months (0=January), which means that an annual timestamp is of the form 2008-10-01 00:00, normally rendered by application software as 2008-2009, and denoting the hydrological year 2008-2009.

timestamp_rounding may be None, meaning that the timestamps can be irregular.

Timestamp_rounding is named differently in older versions. See the Version parameter above for more information.

Timestamp_offset

A comma-separated pair of integers indicating the number of minutes and months that must be added to the nominal timestamp to get to the actual timestamp. The timestamp offset for small time steps, such as up to daily, is usually zero, except if the nominal timestamp is the beginning of an interval, in which case the timestamp offset is equal to the length of the time step, so that the actual timestamp is the end of the interval. For monthly and annual time steps, the timestamp offset is usually 1 and 12 months respectively. For a monthly time series, a timestamp offset of (-475, 1) means that 2003-11-01 00:00 (often rendered as 2003-11) denotes the interval 2003-10-31 18:05 to 2003-11-30 18:05.

Timestamp_offset is named differently in older versions. See the Version parameter above for more information.

Interval_type

Has one of the values sum, average, maximum, minimum, and vector_average. If absent it means that the time series values are instantaneous, they do not refer to intervals.

Variable

A textual description of the variable, such as Temperature or Precipitation.

Precision

The precision of the time series values, in number of decimal digits after the decimal separator. It can be negative; for example, a precision of -2 indicates values accurate to the hundred, such as 100, 200, 300 etc.

Location, Altitude

(Versions 3 and later.) Location is three numbers, space-separated: abscissa, ordinate, and EPSG SRID. Altitude is one or two space-separated numbers: the altitude and the EPSG SRID for altitude. The altitude SRID may be omitted.

License

Written by Antonis Christofides.

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program. If not, see <http://www.gnu.org/licenses/>.