# Table numpy vs dimarrayΒΆ

Table of correspondence between numpy ndarray and dimarray’s functions and methods

array creation | ||
---|---|---|

numpy | dimarray | comments |

array | DimArray | In dimarray need to provide axes information in addition to values. |

DimArray.from_kw | Same as DimArray() but provide axes as key-words. | |

array | same as DimArray() | |

array_kw | same as DimArray.from_kw() | |

zeros | zeros | These functions are similar to numpy except that they require axes parameter, or a shape= parameter for automatic labelling. |

ones | ones | |

empty | empty | |

zeros_like | zeros_like | |

ones_like | ones_like | |

empty_like | empty_like |

Note

The array and array_kw forms (to be used as da.array()) are attempts to make the array definition less verbose. They are experimental and may change in the future.

reshaping | ||
---|---|---|

numpy | dimarray | comments |

a.T | a.T | Transpose a 2-dimensional array |

a.transpose() | a.transpose() | Transpose or permute array. In dimarray also accept axis names |

a.swapaxes() | a.swapaxes() | Swap two axes. In dimarray also accept axis names. e.g. a.swapaxes(‘time’, 0) to bring the ‘time’ dimension as first axis to ease indexing. |

a.reshape() | a.reshape() | Change array shape without changing the size. There are a few differences in dimarray compared to numpy: - a dimension cannot be broken down (e.g. 4 => 2x2) - the full shape of the array is given via axis names e.g. a.reshape(‘time,percentile’,’scenario’) will flatten (group) the dimensions time and percentile to end up with a 2-D array, and transpose the array as necessary to get to the desired shape. If only transposing (permutation) is needed, the use of transpose is preferred for clarity. |

a.group() | Flatten two axes into one: it is for reshape what swapaxes is to transpose. | |

a.ungroup() | Inflate two or more “grouped” axes (undo a.group()). | |

a.flatten() | a.flatten() | Flatten array. In dimarray the axes are transformed into tuples (GroupedAxis). |

a[np.newaxis] | a.newaxis() | In numpy, add a singleton dimension, useful for broadcasting in an operation. In dimarray, broadcasting is based on dimension names and therefore streamlined without the need to profide this extra-information, make this option less relevant in the public API. In dimarray this is a method since it requires the name of the new axis, and by extension, if the new axis’ values are also provided it can also combines functionality of repeat. |

a.squeeze() | a.squeeze() | idem, but also accept axis names (opposite of newaxis) |

a.repeat() | a.repeat() | In dimarray it’s mostly an internal method that only works on singleton dimensions. This is of no much practical use. Use newaxis instead. |

broadcast() | a.broadcast() | Dimarray’s method similar to numpy’s function. Add or remove singleton axes to make it match another array’s
dimensions, but without repeating
(so that the shapes do not necessarily match, but it is ready for binary operations in a numpy sense)
In dimarray, the broadcast method can also transpose axes to match dimension ordering. |

broadcast_arrays() | broadcast_arrays() | Functions. Like the above, but also repeat the arrays if necessary to match the shape. |

Note

The names group and ungroup may be confusing and could change in the future (e.g. to flatten and inflate, or unflatten)

The methods below are mostly similar across the packages, but dimarray also accepts axis name instead of axis rank as axis=. An optional skipna= parameter can be provided to ignore nans (default to False). Note also that in many cases, when a tuple of axis names is provided the array is first partially flattened (grouped axis) before the dimension is reduced

reduce, accumulate (along-axis transformation) | ||
---|---|---|

numpy | dimarray | comments |

a.max() | a.max() | |

a.min() | a.min() | |

a.ptp() | a.ptp() | |

a.median() | a.median() | |

a.all() | a.all() | |

a.any() | a.any() | |

a.prod() | a.prod() | |

a.sum() | a.sum() | |

a.mean() | a.mean() | with optional “weights=” parameter to transform into a weighted mean, which is also checked from Axis attribute. |

a.std() | a.std() | idem |

a.var() | a.var() | idem |

a.argmax() | a.argmax() | in dimarray, returns axis value of max instead of integer position on the axis |

a.argmin() | a.argmin() | idem |

a.cumsum() | a.cumsum() | |

a.cumprod() | a.cumprod() | |

diff(a,...) | a.diff() | as method, and with scheme= parameter (“forward”, “centered”, “backward”) |