# 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: astropy.table.column.BaseColumn

Define a data column for use in a Table object.

Parameters
datalist, ndarray or None

Column data values

namestr

Column name and key for reference within Table

dtypenumpy.dtype compatible value

Data type for column

shapetuple or ()

Dimensions of a single row element in the column data

lengthint or 0

Number of row elements in column data

descriptionstr or None

Full description of column

unitstr or None

Physical unit

formatstr or None or function or 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.

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.

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_unitstr or astropy.units.UnitBase instance

The unit to convert to.

equivalencieslist of equivalence pairs, optional

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

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
objint, slice or sequence of ints

Object that defines the index or indices before which values is inserted.

valuesarray_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.

axisint, 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_linesint

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_linesint

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
lineslist

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_linesint

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
unitUnit or str

The unit to convert to (i.e., a valid argument to the astropy.units.Quantity.to() method).

equivalencieslist of equivalence pairs, optional

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.