The .push method can take multiple arguments. You can use the spread operator to pass all the elements of the second array as arguments to .push: >>> a.push(…b) If your browser does not support ECMAScript 6, you can use .apply instead: >>> a.push.apply(a, b) Or perhaps, if you think it’s clearer: >>> Array.prototype.push.apply(a,b) Please note … Read more
The best way of appending a string to a string variable is to use + or +=. This is because it’s readable and fast. They are also just as fast, which one you choose is a matter of taste, the latter one is the most common. Here are timings with the timeit module: a = … Read more
Between those two syntaxes, you should really choose the one you prefer 🙂 Personally, I would go with your second solution in such a case (Variable interpolation), which I find easier to both write and read. The result will be the same; and even if there are performance implications, those won’t matter 1. As a … Read more
SELECT id, GROUP_CONCAT(name SEPARATOR ‘ ‘) FROM table GROUP BY id; https://dev.mysql.com/doc/refman/8.0/en/aggregate-functions.html#function_group-concat From the link above, GROUP_CONCAT: This function returns a string result with the concatenated non-NULL values from a group. It returns NULL if there are no non-NULL values.
This should do it For large files: filenames = [‘file1.txt’, ‘file2.txt’, …] with open(‘path/to/output/file’, ‘w’) as outfile: for fname in filenames: with open(fname) as infile: for line in infile: outfile.write(line) For small files: filenames = [‘file1.txt’, ‘file2.txt’, …] with open(‘path/to/output/file’, ‘w’) as outfile: for fname in filenames: with open(fname) as infile: outfile.write(infile.read()) … and another … Read more
In C, “strings” are just plain char arrays. Therefore, you can’t directly concatenate them with other “strings”. You can use the strcat function, which appends the string pointed to by src to the end of the string pointed to by dest: char *strcat(char *dest, const char *src); Here is an example from cplusplus.com: char str[80]; … Read more
Let’s call your data.frame DF > aggregate(id ~ brand, data = DF, c) brand id 1 RadioShack 2308 2 Rag & Bone 4466 3 Ragu 1830, 4518 4 Ralph Lauren 1638, 2719, 2720, 2721, 2722 Another alternative using aggregate is: result <- aggregate(id ~ brand, data = DF, paste, collapse = “,”) This produces the … Read more
Standard C Preprocessor $ cat xx.c #define VARIABLE 3 #define PASTER(x,y) x ## _ ## y #define EVALUATOR(x,y) PASTER(x,y) #define NAME(fun) EVALUATOR(fun, VARIABLE) extern void NAME(mine)(char *x); $ gcc -E xx.c # 1 “xx.c” # 1 “<built-in>” # 1 “<command-line>” # 1 “xx.c” extern void mine_3(char *x); $ Two levels of indirection In a comment … Read more
Never call DataFrame.append or pd.concat inside a for-loop. It leads to quadratic copying. pd.concat returns a new DataFrame. Space has to be allocated for the new DataFrame, and data from the old DataFrames have to be copied into the new DataFrame. Consider the amount of copying required by this line inside the for-loop (assuming each … Read more
The problem here is that the + operator has (at least) two different meanings in Python: for numeric types, it means “add the numbers together”: >>> 1 + 2 3 >>> 3.4 + 5.6 9.0 … and for sequence types, it means “concatenate the sequences”: >>> [1, 2, 3] + [4, 5, 6] [1, 2, … Read more