Extracting specific columns in numpy array

Question

This is an easy question but say I have an MxN matrix  All I want to do is extract specific columns and store them in another numpy array but I get invalid syntax errors  Here is the code   extractedData   data    1     9       It seems like the above line should suffice but I guess not  I looked around but couldn t find anything syntax wise regarding this specific scenario

User · Answer

One more thing you should pay attention to when selecting columns from N-D array using a list like this:

data[:,:,[1,9]]

If you are removing a dimension (by selecting only one row, for example), the resulting array will be (for some reason) permuted. So:

print data.shape            # gives [10,20,30]
selection = data[1,:,[1,9]]
print selection.shape       # gives [2,20] instead of [20,2]!!

User · Answer

I think the solution here is not working with an update of the python version anymore  one way to do it with a new python function for it is   extracted data   data   Column Name1   Column Name2    to numpy     which gives you the desired outcome   The documentation you can find here  https   pandas pydata org pandas-docs stable reference api pandas DataFrame to numpy html pandas DataFrame to numpy

User · Answer

Assuming you want to get columns 1 and 9 with that code snippet  it should be   extractedData   data    1 9

User · Answer

you can also use extractedData data    1     9

User · Answer

You can use the following  extracted data   data ix     Column1   Column2

User · Answer

I assume you wanted columns 1 and 9  To select multiple columns at once  use X   data     1  9    To select one at a time  use x  y   data    1   data    9    With names  data      Column Name1   Column Name2     You can get the names from data dtype names

User · Answer

One thing I would like to point out is  if the number of columns you want to extract is 1 the resulting matrix would not be a Mx1 Matrix as you might expect but instead an array containing the elements of the column you extracted   To convert it to Matrix the reshape M 1  method should be used on the resulting array

User · Answer

if you want to extract only some columns   idx IN columns    1  9  extractedData   data   idx IN columns    if you want to exclude specific columns   idx OUT columns    1  9  idx IN columns    i for i in xrange np shape data  1   if i not in idx OUT columns  extractedData   data   idx IN columns

User · Answer

Just    gt  gt  gt  m   np matrix np random random  5  5     gt  gt  gt  m matrix   0 91074101  0 65999332  0 69774588  0 007355    0 33025395            0 11078742  0 67463754  0 43158254  0 95367876  0 85926405            0 98665185  0 86431513  0 12153138  0 73006437  0 13404811            0 24602225  0 66139215  0 08400288  0 56769924  0 47974697            0 25345299  0 76385882  0 11002419  0 2509888   0 06312359     gt  gt  gt  m    1  2   matrix   0 65999332  0 69774588            0 67463754  0 43158254            0 86431513  0 12153138            0 66139215  0 08400288            0 76385882  0 11002419      The columns need not to be in order    gt  gt  gt  m    2  1  3   matrix   0 69774588  0 65999332  0 007355              0 43158254  0 67463754  0 95367876            0 12153138  0 86431513  0 73006437            0 08400288  0 66139215  0 56769924            0 11002419  0 76385882  0 2509888

[python] Extracting specific columns in numpy array

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