concatenation

Consider the following scenario: std::vector<int> A; std::vector<int> B; std::vector<int> AB; I want AB to have contents of A and then the contents of B in the same order. Approach 1: AB.reserve( A.size() + B.size() ); // preallocate memory AB.insert( AB.end(), A.begin(), A.end() ); AB.insert( AB.end(), B.begin(), B.end() ); Approach 2: std::vector<int> AB ( A.begin(), A.end() ); // calling constructor AB.insert ( AB.end(), B.begin(), B.end() ); Which one of the above methods is more efficient? Why? Is there a different method that is more efficient? I think the first one will always be faster

I want equivalent to GROUP_CONCAT functionality of MySql in DB2. I have tried XML Aggrigate functon of DB2 for cocating murows. SELECT a.ID, substr(xmlserialize(xmlagg(xmltext( concat(',', SPECIALISATION)))as varchar( 1024 )),2), substr(xmlserialize(xmlagg(xmltext(concat(',,, BASIC_SKILL2)))as varchar( 1024 )),2), substr(xmlserialize(xmlagg(xmltext(concat(',', BASIC_SKILL1)))as varchar( 1024 )),2) FROM candidate_resume_data a,candidate_skills_info b,skill_special_master c,skill_master_basic2 d,skill_master_basic1 e WHERE e.SKILL_BASIC1_ID = d.SKILL_BASIC1_ID AND b.ID = a.ID AND d.SKILL_BASIC2

i was wondering if there was a way to add a value to a string, not like 1 + 1 = 2 but like 1 + 1 = 11. I think you need string concatenation: #include <stdio.h> #include <string.h> int main() { char str1[50] = "Hello "; char str2[] = "World"; strcat(str1, str2); printf("str1: %s\n", str1); return 0; } from: http://irc.essex.ac.uk/www.iota-six.co.uk/c/g6_strcat_strncat.asp To concatenate more than two strings, you can use sprintf, e.g. char buffer[101]; sprintf(buffer, "%s%s%s%s", "this", " is", " my", " story"); Try taking a look at the strcat API. With sufficient buffer space, you can add one

I am trying to concat two dataframe, horizontally. df2 contains 2 result variables for every observation in df1. df1.shape (242583, 172) df2.shape (242583, 2) My code is: Fin = pd.concat([df1, df2], axis= 1) But somehow the result is stacked in 2 dimensions: Fin.shape (485166, 174) What am I missing here? There are different index values, so indexes are not aligned and get NaN s: df1 = pd.DataFrame({ 'A': ['a','a','a'], 'B': range(3) }) print (df1) A B 0 a 0 1 a 1 2 a 2 df2 = pd.DataFrame({ 'C': ['b','b','b'], 'D': range(4,7) }, index=[5,7,8]) print (df2) C D 5 b 4 7 b 5 8 b 6 Fin = pd.concat(

I have two arrays a & b a.shape (5, 4, 3) array([[[ 0. , 0. , 0. ], [ 0. , 0. , 0. ], [ 0. , 0. , 0. ], [ 0.10772717, 0.604584 , 0.41664413]], [[ 0. , 0. , 0. ], [ 0. , 0. , 0. ], [ 0.10772717, 0.604584 , 0.41664413], [ 0.95879616, 0.85575133, 0.46135877]], [[ 0. , 0. , 0. ], [ 0.10772717, 0.604584 , 0.41664413], [ 0.95879616, 0.85575133, 0.46135877], [ 0.70442301, 0.74126523, 0.88965603]], [[ 0.10772717, 0.604584 , 0.41664413], [ 0.95879616, 0.85575133, 0.46135877], [ 0.70442301, 0.74126523, 0.88965603], [ 0.8039435 , 0.62802183, 0.58885027]], [[ 0.95879616, 0.85575133, 0.46135877], [ 0