# All Questions

1,796 questions

**158**

votes

**20**answers

70k views

### Find unique rows in numpy.array

I need to find unique rows in a numpy.array.For example:>>> a # I havearray([[1, 1, 1, 0, 0, 0],[0, 1, 1, 1, 0, 0],[0, 1, 1, 1, 0, 0],[1, 1, 1, 0, 0, 0],[...

**106**

votes

**9**answers

78k views

### Using numpy to build an array of all combinations of two arrays

I'm trying to run over the parameters space of a 6 parameter function to study it's numerical behavior before trying to do anything complex with it so I'm searching for a efficient way to do this.My ...

**9**

votes

**5**answers

4k views

### Find the row indexes of several values in a numpy array

I have an array X:X=np.array([[4, 2],[9, 3],[8, 5],[3, 3],[5, 6]])And I wish to find the index of the row of several values in ...

**266**

votes

**12**answers

200k views

### Check if multiple strings exist in another string

How can I check if any of the strings in an array exists in another string?Like:a=['a', 'b', 'c']str="a123"if a in str:print "some of the strings found in str"else:print "no strings ...

**280**

votes

**4**answers

104k views

### What are the differences between numpy arrays and matrices? Which one should I use?

What are the advantages and disadvantages of each?From what I've seen, either one can work as a replacement for the other if need be, so should I bother using both or should I stick to just one of ...

**228**

votes

**9**answers

198k views

### Sorting arrays in NumPy by column

How can I sort an array in NumPy by the nth column?For example,a=array([[9, 2, 3],[4, 5, 6],[7, 0, 5]])I'd like to sort rows by the second column, such that I get back:...

**132**

votes

**7**answers

51k views

### How is Python's List Implemented?

Is it a linked list, an array? I searched around and only found people guessing. My C knowledge isn't good enough to look at the source code.

**382**

votes

**13**answers

339k views

### How to print the full NumPy array?

When I print a numpy array, I get a truncated representation, but I want the full array. Is there any way to do this?Examples:>>> numpy.arange(10000)array([ 0, 1, 2, ..., 9997, ...

**106**

votes

**5**answers

492k views

### ValueError: setting an array element with a sequence

This Python code:import numpy as pdef firstfunction():UnFilteredDuringExSummaryOfMeansArray=[]MeanOutputHeader=['TestID','ConditionName','FilterType','RRMean','HRMean','...

**96**

votes

**9**answers

127k views

### How Big can a Python Array Get?

In Python, how big can an array/list get? I need an array of about 12000 elements. Will I still be able to run array/list methods such as sorting, etc?

**340**

votes

**13**answers

448k views

### Is there a NumPy function to return the first index of something in an array?

I know there is a method for a Python list to return the first index of something:>>> l=list([1, 2, 3])>>> l.index(2)1Is there something like that for NumPy arrays?

**46**

votes

**6**answers

21k views

### Numpy `logical_or` for more than two arguments

Numpy's logical_or function takes no more than two arrays to compare. How can I find the union of more than two arrays? (The same question could be asked with regard to Numpy's logical_and and ...

**306**

votes

**9**answers

268k views

### Python List vs. Array - when to use?

If you are creating a 1d array, you can implement it as a List, or else use the 'array' module in the standard library. I have always used Lists for 1d arrays.What is the reason or circumstance ...

**131**

votes

**10**answers

227k views

### convert a string of bytes into an int (python)

How can I convert a string of bytes into an int in python? Say like this: 'y\xcc\xa6\xbb'I came up with a clever/stupid way of doing it:sum(ord(c) << (i * 8) for i, c in enumerate('y\xcc\...

**83**

votes

**8**answers

107k views

### How to find list intersection?

a=[1,2,3,4,5]b=[1,3,5,6]c=a and bprint cactual output: [1,3,5,6]expected output: [1,3,5]How can we achieve a boolean AND operation (list intersection) on two lists?

**108**

votes

**8**answers

200k views

### hexadecimal string to byte array in python

I have a long Hex string that represents a series of values of different types. I wish to convert this Hex String into a byte array so that I can shift each value out and convert it into its proper ...

**19**

votes

**2**answers

22k views

### Computing the correlation coefficient between two multi-dimensional arrays

I have two arrays that have the shapes N X T and M X T. I'd like to compute the correlation coefficient across T between every possible pair of rows n and m (from N and M, respectively).What's the ...

**66**

votes

**3**answers

8k views

### Why is numpy's einsum faster than numpy's built in functions?

Lets start with three arrays of dtype=np.double. Timings are performed on a intel CPU using numpy 1.7.1 compiled with icc and linked to intel's mkl. A AMD cpu with numpy 1.6.1 compiled with gcc ...

**32**

votes

**2**answers

31k views

### Store different datatypes in one NumPy array?

I have two different arrays, one with strings and another with ints. I want to concatenate them, into one array where each column has the original datatype. My current solution for doing this (see ...

**371**

votes

**9**answers

383k views

### Dump a NumPy array into a csv file

Is there a way to dump a NumPy array into a CSV file? I have a 2D NumPy array and need to dump it in human-readable format.

**154**

votes

**14**answers

167k views

### numpy: most efficient frequency counts for unique values in an array

In numpy / scipy, is there an efficient way to get frequency counts for unique values in an array?Something along these lines:x=array( [1,1,1,2,2,2,5,25,1,1] )y=freq_count( x )print y>&...

**91**

votes

**6**answers

504k views

### How to read a text file into a list or an array with Python

I am trying to read the lines of a text file into a list or array in python. I just need to be able to individually access any item in the list or array after it is created.The text file is ...

**24**

votes

**2**answers

7k views

### Set partitions in Python

I have an array of [1,2,3]I want to make all the possible combinations using all elements of the array:Result:[[1], [2], [3]][[1,2], [3]][[1], [2,3]][[1,3], [2]][[1,2,3]]

**32**

votes

**6**answers

24k views

### How to apply a disc shaped mask to a numpy array?

I have an array like this:>>> np.ones((8,8))array([[ 1., 1., 1., 1., 1., 1., 1., 1.],[ 1., 1., 1., 1., 1., 1., 1., 1.],[ 1., 1., 1., 1., 1., 1., 1., 1.]...

**157**

votes

**4**answers

209k views

### Comparing two numpy arrays for equality, element-wise

What is the simplest way to compare two numpy arrays for equality (where equality is defined as: A=B iff for all indices i: A[i] ==B[i])?Simply using==gives me a boolean array:>>> ...

**200**

votes

**11**answers

462k views

### Convert pandas dataframe to numpy array, preserving index

I am interested in knowing how to convert a pandas dataframe into a numpy array, including the index, and set the dtypes.dataframe:import numpy as npimport pandas as pdindex=[1, 2, 3, 4, 5, 6,...

**113**

votes

**4**answers

27k views

### Understanding NumPy's einsum

I'm struggling to understand exactly how einsum works. I've looked at the documentation and a few examples, but it's not seeming to stick.Here's an example we went over in class:C=np.einsum("ij,...

**117**

votes

**9**answers

166k views

### Numpy matrix to array

I am using numpy. I have a matrix with 1 column and N rows and I want to get an array from with N elements.For example, if i have M=matrix([[1], [2], [3], [4]]), I want to get A=array([1,2,3,4])....

**16**

votes

**5**answers

3k views

### Convert Python sequence to NumPy array, filling missing values

The implicit conversion of a Python sequence of variable-length lists into a NumPy array cause the array to be of type object.v=[[1], [1, 2]]np.array(v)>>> array([[1], [1, 2]], dtype=...

**124**

votes

**7**answers

230k views

### how does multiplication differ for NumPy Matrix vs Array classes?

The numpy docs recommend using array instead of matrix for working with matrices. However, unlike octave (which I was using till recently), * doesn't perform matrix multiplication, you need to use the ...