Column¶

class astropy.table.Column(data=None, name=None, dtype=None, shape=(), length=0, description=None, unit=None, format=None, meta=None, copy=False, copy_indices=True)[source]¶

Bases: BaseColumn

Define a data column for use in a Table object.

Parameters:

datapython:list, ndarray, or python:None: Column data values
namepython:str: Column name and key for reference within Table
dtypedtypeastropy:-like: Data type for column
shapepython:tuple or (): Dimensions of a single row element in the column data
lengthpython:int or 0: Number of row elements in column data
descriptionpython:str or python:None: Full description of column
unitpython:str or python:None: Physical unit
formatpython:str, python:None, or python:callable(): Format string for outputting column values. This can be an “old-style” (format % value) or “new-style” (str.format) format specification string or a function or any callable object that accepts a single value and returns a string.
metadict-like or python:None: Meta-data associated with the column

Examples

A Column can be created in two different ways:

Provide a data value but not shape or length (which are inferred from the data).

Examples:
```
col = Column(data=[1, 2], name='name')  # shape=(2,)
col = Column(data=[[1, 2], [3, 4]], name='name')  # shape=(2, 2)
col = Column(data=[1, 2], name='name', dtype=float)
col = Column(data=np.array([1, 2]), name='name')
col = Column(data=['hello', 'world'], name='name')
```
The dtype argument can be any value which is an acceptable fixed-size data-type initializer for the numpy.dtype() method. See https://numpy.org/doc/stable/reference/arrays.dtypes.html. Examples include:
- Python non-string type (float, int, bool)
- Numpy non-string type (e.g. np.float32, np.int64, np.bool_)
- Numpy.dtype array-protocol type strings (e.g. ‘i4’, ‘f8’, ‘S15’)
If no dtype value is provide then the type is inferred using np.array(data).
Provide length and optionally shape, but not data

Examples:
```
col = Column(name='name', length=5)
col = Column(name='name', dtype=int, length=10, shape=(3,4))
```
The default dtype is np.float64. The shape argument is the array shape of a single cell in the column.

To access the Column data as a raw numpy.ndarray object, you can use one of the data or value attributes (which are equivalent):

col.data
col.value

Attributes Summary

`name`	The name of this column.
`quantity`	A view of this table column as a `Quantity` object with units given by the Column's `unit` parameter.
`unit`	The unit associated with this column.

Methods Summary

`convert_unit_to`(new_unit[, equivalencies])	Converts the values of the column in-place from the current unit to the given unit.
`copy`([order, data, copy_data])	Return a copy of the current instance.
`insert`(obj, values[, axis])	Insert values before the given indices in the column and return a new `Column` object.
`more`([max_lines, show_name, show_unit])	Interactively browse column with a paging interface.
`pformat`([max_lines, show_name, show_unit, ...])	Return a list of formatted string representation of column values.
`pprint`([max_lines, show_name, show_unit, ...])	Print a formatted string representation of column values.
`to`(unit[, equivalencies])	Converts this table column to a `Quantity` object with the requested units.

Attributes Documentation

name¶: The name of this column.

quantity¶: A view of this table column as a Quantity object with units given by the Column’s unit parameter.

unit¶

The unit associated with this column. May be a string or a astropy.units.UnitBase instance.

Setting the unit property does not change the values of the data. To perform a unit conversion, use convert_unit_to.

Methods Documentation

convert_unit_to(new_unit, equivalencies=[])¶

Converts the values of the column in-place from the current unit to the given unit.

To change the unit associated with this column without actually changing the data values, simply set the unit property.

Parameters:

new_unitpython:str or astropy.units.UnitBase instance: The unit to convert to.
equivalenciespython:list of python:tuple: A list of equivalence pairs to try if the unit are not directly convertible. See Equivalencies.

Raises:

astropy.units.UnitsError: If units are inconsistent

copy(order='C', data=None, copy_data=True)¶

Return a copy of the current instance.

If data is supplied then a view (reference) of data is used, and copy_data is ignored.

Parameters:

order{‘C’, ‘F’, ‘A’, ‘K’}, optional: Controls the memory layout of the copy. ‘C’ means C-order, ‘F’ means F-order, ‘A’ means ‘F’ if a is Fortran contiguous, ‘C’ otherwise. ‘K’ means match the layout of a as closely as possible. (Note that this function and :func:numpy.copy are very similar, but have different default values for their order= arguments.) Default is ‘C’.
dataarray, optional: If supplied then use a view of data instead of the instance data. This allows copying the instance attributes and meta.
copy_databool, optional: Make a copy of the internal numpy array instead of using a reference. Default is True.

Returns:

colColumn or MaskedColumn: Copy of the current column (same type as original)

insert(obj, values, axis=0)[source]¶

Insert values before the given indices in the column and return a new Column object.

Parameters:

objpython:int, slice or python:sequence of python:int: Object that defines the index or indices before which values is inserted.
valuesnumpy:array_like: Value(s) to insert. If the type of values is different from that of the column, values is converted to the matching type. values should be shaped so that it can be broadcast appropriately.
axispython:int, optional: Axis along which to insert values. If axis is None then the column array is flattened before insertion. Default is 0, which will insert a row.

Returns:

outColumn: A copy of column with values and mask inserted. Note that the insertion does not occur in-place: a new column is returned.

more(max_lines=None, show_name=True, show_unit=False)¶

Interactively browse column with a paging interface.

Supported keys:

f, <space> : forward one page
b : back one page
r : refresh same page
n : next row
p : previous row
< : go to beginning
> : go to end
q : quit browsing
h : print this help

Parameters:

max_linespython:int: Maximum number of lines in table output.
show_namebool: Include a header row for column names. Default is True.
show_unitbool: Include a header row for unit. Default is False.

pformat(max_lines=None, show_name=True, show_unit=False, show_dtype=False, html=False)¶

Return a list of formatted string representation of column values.

If no value of max_lines is supplied then the height of the screen terminal is used to set max_lines. If the terminal height cannot be determined then the default will be determined using the astropy.conf.max_lines configuration item. If a negative value of max_lines is supplied then there is no line limit applied.

Parameters:

max_linespython:int: Maximum lines of output (header + data rows)
show_namebool: Include column name. Default is True.
show_unitbool: Include a header row for unit. Default is False.
show_dtypebool: Include column dtype. Default is False.
htmlbool: Format the output as an HTML table. Default is False.

Returns:

linespython:list: List of lines with header and formatted column values

pprint(max_lines=None, show_name=True, show_unit=False, show_dtype=False)¶

Print a formatted string representation of column values.

If no value of max_lines is supplied then the height of the screen terminal is used to set max_lines. If the terminal height cannot be determined then the default will be determined using the astropy.conf.max_lines configuration item. If a negative value of max_lines is supplied then there is no line limit applied.

Parameters:

max_linespython:int: Maximum number of values in output
show_namebool: Include column name. Default is True.
show_unitbool: Include a header row for unit. Default is False.
show_dtypebool: Include column dtype. Default is True.

to(unit, equivalencies=[], **kwargs)¶

Converts this table column to a Quantity object with the requested units.

Parameters:

unitastropy:unit-like: The unit to convert to (i.e., a valid argument to the astropy.units.Quantity.to() method).
equivalenciespython:list of python:tuple: Equivalencies to use for this conversion. See astropy.units.Quantity.to() for more details.

Returns:

quantityQuantity: A quantity object with the contents of this column in the units unit.

Navigation

Column¶