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How do I append one string to another in Python?
...
If you only have one reference to a string and you concatenate another string to the end, CPython now special cases this and tries to extend the string in place.
The end result is that the operation is amortized O(n).
e.g.
s = ""
for i in range(n):
s+=str(i)
used to ...
Pandas groupby: How to get a union of strings
...is!
3 3 0.463468 a
4 4 0.643961 random
sum by default concatenates
In [9]: df.groupby('A')['C'].apply(lambda x: x.sum())
Out[9]:
A
1 Thisstring
2 is!
3 a
4 random
dtype: object
You can do pretty much what you want
In [11]: df.groupby('A')['C'...
Transposing a 2D-array in JavaScript
...rix.reduce((prev, next) => next.map((item, i) =>
(prev[i] || []).concat(next[i])
), []);
}
Lodash/Underscore by marcel
function tranpose(matrix) {
return _.zip(...matrix);
}
// Without spread operator.
function transpose(matrix) {
return _.zip.apply(_, [[1,2,3], [1,2,3], [1,2,3]]...
Creating an empty Pandas DataFrame, then filling it?
...ire handling the index appropriately).
Things you should NOT do
append or concat inside a loop
Here is the biggest mistake I've seen from beginners:
df = pd.DataFrame(columns=['A', 'B', 'C'])
for a, b, c in some_function_that_yields_data():
df = df.append({'A': i, 'B': b, 'C': c}, ignore_index=...
How do I create a PDO parameterized query with a LIKE statement?
...e LIKE with % partial matching for MySQL databases: WHERE column_name LIKE CONCAT('%', :dangerousstring, '%')
where the named parameter is :dangerousstring.
In other words, use explicitly unescaped % signs in your own query that are separated and definitely not the user input.
Edit: Concatenati...
When to use StringBuilder in Java [duplicate]
...is supposed to be generally preferable to use a StringBuilder for string concatenation in Java. Is this always the case?
...
erb, haml or slim: which one do you suggest? And why? [closed]
...s in smaller screens
visually cleaner structure
has built in helpers (haml_concat, haml_capture) to utilize haml in helper methods
class chaining
lots of useful syntactic sugar like # for divs or . for class chaining, or :javascript for JS tags
Cons
whitespace dependent which makes for some har...
How does the String class override the + operator?
...ls of the string conversion context.
15.18.1.
Optimization of String Concatenation :
An implementation may choose to perform conversion and concatenation
in one step to avoid creating and then discarding an intermediate
String object. To increase the performance of repeated string
conc...
Return multiple columns from pandas apply()
... series, new columns exist):')
df_test = create_new_df_test()
df_test = pd.concat([df_test, pd.DataFrame(columns=['size_kb', 'size_mb', 'size_gb'])])
%timeit result = df_test.apply(sizes_pass_series_return_series, axis=1)
print('\nPandafied (pass series, return tuple, new columns dont exist):')
df_...
how to split the ng-repeat data with three columns using bootstrap
...d format:
$scope.$watch('chunkedData', function(val) {
$scope.data = [].concat.apply([], val);
}, true); // deep watch
Many people prefer to accomplish this in the view with a filter. This is possible, but should only be used for display purposes! If you add inputs within this filtered view, it...