menu

login

Log in

Linear Algebra

Prob and Stats

Other math topics

Machine Learning

Dagster (NEW)

search

Search

Login

Unlock 100+ guides

menu

menu

search toc

close

Outline

Parameters Return value Examples Compressing a 1D array Truncation Compressing a 2D array Extracting from a flattened array Extracting row-wise Extracting column-wise

Comments

Log in or sign up

Cancel

Post

account_circle

exit_to_app

Sign out

What does this mean?

Why is this true?

Give me some examples!

search

keyboard_voice

close

Searching Tips

Search for a recipe:
"Creating a table in MySQL"

Search for an API documentation: "@append"

Search for code: "!dataframe"

Apply a tag filter: "#python"

Useful Shortcuts

/ to open search panel

Esc to close search panel

↑↓ to navigate between search results

⌘d to clear all current filters

⌘Enter to expand content preview

icon_star

Doc Search

icon_star

Code Search Beta

SORRY NOTHING FOUND!

mic

Start speaking...

Voice search is only supported in Safari and Chrome.

fullscreen_exit

Shrink

Navigate to

NumPy

319 guides

keyboard_arrow_down

Linear Algebra

Prob and Stats

Machine Learning

Other math topics

chevron_leftDocumentation

Method argpartition

NumPy Random Generator4 topics

Method choice Method dot Method finfo Method histogram Method iinfo Method max Method mean Method place Method roots Method seed Method uniform Method view Method zeros Method sum Object busdaycalendar Method is_busday Property dtype Method unique Method loadtxt Method vsplit Method fliplr Method setdiff1d Method msort Method argsort Method lexsort Method around Method nanmax Method nanmin Method nanargmax Method nanargmin Method argmax Method argmin Property itemsize Method spacing Method fix Method ceil Method diff Property flat Property real Property base Method flip Method delete Method amax Method amin Method logical_xor Method logical_or Method logical_not Method logical_and Method logaddexp Method logaddexp2 Method logspace Method not_equal Method equal Method greater_equal Method less Method less_equal Method remainder Method mod Method empty Method greater Method isfinite Method busday_count Method repeat Method var Method random_sample Method random Method sign Method std Method absolute Method abs Method sort Method randint Method isreal Method linspace Method gradient Method all Method sample Property T Property imag Method cov Method insert Method log Method log1p Method exp2 Method expm1 Method exp Method arccos Method cos Method arcsin Method sin Method tan Method fromiter Method trim_zeros Method diagflat Method savetxt Method count_nonzero Property size Property shape Method reshape Method resize Method triu Method tril Method eye Method arange Method fill_diagonal Method tile Method save Method transpose Method swapaxes Method meshgrid Property mgrid Method rot90 Method log2 Method radians Method deg2rad Method rad2deg Method degrees Method log10 Method append Method cumprod Property nbytes Method tostring Property data Method modf Method fmod Method tolist Method datetime_as_string Method datetime_data Method array_split Method itemset Method floor Method put_along_axis Method cumsum Method bincount Method put Method putmask Method take Method hypot Method sqrt Method square Method floor_divide Method tri Method signbit Method flatten Method ravel Method roll Method isrealobj Method diag Method diagonal Method quantile Method ones Method iscomplexobj Method iscomplex Method isscalar Method divmod Method isnat Method percentile Method isnan Method divide Method add Method reciprocal Method positive Method subtract Method median Method isneginf Method isposinf Method float_power Method power Method negative Method maximum Method average Method isinf Method multiply Method busday_offset Method identity Method interp Method squeeze Method get_printoptions Method savez_compressed Method savez Method load Method asfarray Method clip Method array Method array_equiv Method array_equal Method frombuffer Method set_string_function Method matmul Method genfromtxt Method fromfunction Method asscalar Method searchsorted Method full_like Method full Method shares_memory Method ptp Method digitize Method argwhere Method geomspace Method zeros_like Method fabs Method flatnonzero Method vstack Method dstack Method fromstring Method tobytes Method expand_dims Method ranf Method arctan Method item Method extract Method compress Method choose Method asarray Method asmatrix Method allclose Method isclose Method any Method corrcoef Method trunc Method prod Method cross Method true_divide Method hsplit Method split Method rint Method ediff1d Method lcm Method gcd Method cbrt Method flipud Property ndim Method array2string Method set_printoptions Method where Method hstack

Char32 topics

check_circle

Mark as learned

thumb_up

1

thumb_down

0

chat_bubble_outline

0

Comment

auto_stories Bi-column layout

settings

NumPy | compress method

schedule Aug 12, 2023

Last updated

local_offer

Python●NumPy

Tags

tocTable of Contents

expand_more

Parameters Return value Examples Compressing a 1D array Truncation Compressing a 2D array Extracting from a flattened array Extracting row-wise Extracting column-wise

Master the mathematics behind data science with 100+ top-tier guides
Start your free 7-days trial now!

NumPy's compress(~) method extracts a subset of the input values based on the given condition.

NOTE

NumPy's extract(~) method is equivalent to the compress(~) when the input array is 1D.

Parameters

1. condition | array-like of boolean

An array of booleans that indicate whether or not to set the value. If the size of condition is smaller than the input array a, then output will be truncated so as to match the size of the condition.

2. a | array-like

The input array.

3. axis | int | optional

The axis along which to extract the values. For 2D arrays, the allowed values are as follows:

Axis	Meaning
0	Extraction is done row-wise.
1	Extraction is done column-wise.
None	The input array is treated as a flattened array.

By default, axis=None.

4. out | Numpy array | optional

A NumPy array to place the extracted subset.

Return value

A new NumPy array holding a subset of input values.

Examples

Compressing a 1D array


        
        
            
                
                
                    np.compress([True, False, True, False], [4,5,6,7])
                
            
            array([4, 6])

Notice that this is equivalent to the following:


        
        
            
                
                
                    a = np.array([4,5,6,7])
mask = [True, False, True, False]
a[mask]
                
            
            array([4, 6])

Truncation

Truncation happens when the size of the condition array is smaller than that of the input array:


        
        
            
                
                
                    a = np.array([4,5,6,7])
np.compress([True, False], a)
                
            
            array([4])

Here, only the first two values in the array are considered - yet only first value is returned since the second value is flagged as False.

Compressing a 2D array

Consider the following 2D array:


        
        
            
                
                
                    a = np.array([[4,5],[6,7]])
a
                
            
            array([[4, 5],
       [6, 7]])

Extracting from a flattened array


        
        
            
                
                
                    np.compress([True, False, False, True], a)
                
            
            array([4, 7])

Extracting row-wise


        
        
            
                
                
                    np.compress([True, False], a, axis=0)
                
            
            array([[4, 5]])

Extracting column-wise


        
        
            
                
                
                    np.compress([True, False], a, axis=1)
                
            
            array([[4],
       [6]])

robocat

Published by Isshin Inada

Edited by 0 others

Did you find this page useful?

thumb_up

thumb_down

Comment

Citation

Ask a question or leave a feedback...

thumb_up

1

thumb_down

0

chat_bubble_outline

0

settings

Enjoy our search

Hit / to insta-search docs and recipes!

Navigation

Contact us

Resources

Python Pandas MySQL Beautiful Soup Matplotlib NumPy PySpark

Community

Join our Discord

Join our newsletter for updates on new comprehensive DS/ML guides

|