sorting

问题 I am trying to understand Space Complexities of different sorting algorithms. http://bigocheatsheet.com/?goback=.gde_98713_member_241501229 from the above link I found that the complexity of bubble sort,insertion and selection sort is O(1) where as quick sort is O(log(n)) and merge sort is O(n). we were actually not allocating extra memory in any of the algorithms. Then why the space complexities are different when we are using the same array to sort them? 回答1: When you run code, memory is

问题 I am trying to understand Space Complexities of different sorting algorithms. http://bigocheatsheet.com/?goback=.gde_98713_member_241501229 from the above link I found that the complexity of bubble sort,insertion and selection sort is O(1) where as quick sort is O(log(n)) and merge sort is O(n). we were actually not allocating extra memory in any of the algorithms. Then why the space complexities are different when we are using the same array to sort them? 回答1: When you run code, memory is

问题 I have an array of one structure like below $array1 = array( [123] => array('1'=>'1','2'=>'3'), [345] => array('1'=>'3','2'=>'5'), [789] => array('1'=>'1','2'=>'5'), [567] => array('1'=>'6','2'=>'5'), ); and another array structure as $array2 = array(567,345,789,123); Now i want to sort this one with php sort function, i mean sort the first array with second one to looks like the desired output something like below $array1 = array( [567] => array('1'=>'6','2'=>'5'), [345] => array('1'=>'3','2

问题 I have an array of one structure like below $array1 = array( [123] => array('1'=>'1','2'=>'3'), [345] => array('1'=>'3','2'=>'5'), [789] => array('1'=>'1','2'=>'5'), [567] => array('1'=>'6','2'=>'5'), ); and another array structure as $array2 = array(567,345,789,123); Now i want to sort this one with php sort function, i mean sort the first array with second one to looks like the desired output something like below $array1 = array( [567] => array('1'=>'6','2'=>'5'), [345] => array('1'=>'3','2

问题 Say I have this file. $ cat a.txt c 1002 4 f 1001 1 d 1003 1 a 1001 3 e 1004 2 b 1001 2 I want to sort it by the second column and then by the third column. Column two are numbers, while column 3 can be treated as string. I know the following command works well. $ sort -k2,2n -k3,3 a.txt f 1001 1 b 1001 2 a 1001 3 c 1002 4 d 1003 1 e 1004 2 However, I think sort -k2n a.txt should also work, while it does not. $ sort -k2n a.txt a 1001 3 b 1001 2 f 1001 1 c 1002 4 d 1003 1 e 1004 2 Seems like

问题 Say I have this file. $ cat a.txt c 1002 4 f 1001 1 d 1003 1 a 1001 3 e 1004 2 b 1001 2 I want to sort it by the second column and then by the third column. Column two are numbers, while column 3 can be treated as string. I know the following command works well. $ sort -k2,2n -k3,3 a.txt f 1001 1 b 1001 2 a 1001 3 c 1002 4 d 1003 1 e 1004 2 However, I think sort -k2n a.txt should also work, while it does not. $ sort -k2n a.txt a 1001 3 b 1001 2 f 1001 1 c 1002 4 d 1003 1 e 1004 2 Seems like

问题 Say I have this file. $ cat a.txt c 1002 4 f 1001 1 d 1003 1 a 1001 3 e 1004 2 b 1001 2 I want to sort it by the second column and then by the third column. Column two are numbers, while column 3 can be treated as string. I know the following command works well. $ sort -k2,2n -k3,3 a.txt f 1001 1 b 1001 2 a 1001 3 c 1002 4 d 1003 1 e 1004 2 However, I think sort -k2n a.txt should also work, while it does not. $ sort -k2n a.txt a 1001 3 b 1001 2 f 1001 1 c 1002 4 d 1003 1 e 1004 2 Seems like

问题 Sorting strings by comparisons (e.g. standard QuickSort + strcmp-like function) may be a bit slow, especially for long strings sharing a common prefix (the comparison function takes O(s) time, where s is the length of string), thus a standard solution has the complexity of O(s * nlog n). Are there any known faster algorithms? 回答1: If you know that the string consist only of certain characters (which is almost always the case), you can use a variant of BucketSort or RadixSort. 回答2: You could

问题 Sorting strings by comparisons (e.g. standard QuickSort + strcmp-like function) may be a bit slow, especially for long strings sharing a common prefix (the comparison function takes O(s) time, where s is the length of string), thus a standard solution has the complexity of O(s * nlog n). Are there any known faster algorithms? 回答1: If you know that the string consist only of certain characters (which is almost always the case), you can use a variant of BucketSort or RadixSort. 回答2: You could

问题 I am attempting to work through Hadley Wickham's R for Data Science and have gotten tripped up on the following question: "How could you use arrange() to sort all missing values to the start? (Hint: use is.na())" I am using the flights dataset included in the nycflights13 package. Given that arrange() sorts all unknown values to the bottom of the dataframe, I am not sure how one would do the opposite across the missing values of all variables. I realize that this question can be answered with