concatenation

问题 I'm trying to concatenate Pandas DataFrame columns with NaN values. In [96]:df = pd.DataFrame({'col1' : ["1","1","2","2","3","3"], 'col2' : ["p1","p2","p1",np.nan,"p2",np.nan], 'col3' : ["A","B","C","D","E","F"]}) In [97]: df Out[97]: col1 col2 col3 0 1 p1 A 1 1 p2 B 2 2 p1 C 3 2 NaN D 4 3 p2 E 5 3 NaN F In [98]: df['concatenated'] = df['col2'] +','+ df['col3'] In [99]: df Out[99]: col1 col2 col3 concatenated 0 1 p1 A p1,A 1 1 p2 B p2,B 2 2 p1 C p1,C 3 2 NaN D NaN 4 3 p2 E p2,E 5 3 NaN F NaN

问题 I have been making a script to display users and make changes to their admin privileges. Here is the code: while ($row= mysql_fetch_assoc($query)) { $uname= $row['username']; $fname= $row['first_name']; $lname= $row['last_name']; $email= $row['email']; $admin= $row['admin']; $insert .= '<tr> <td>' .$uname. '</td> <td>' .$fname. '</td> <td>' .$lname. '</td> <td>' .((isset($email)) ? $email:'No email set.'). '</td> <td>'.(($admin == 'y') ? 'Admin':'User').'</td> <td><input type="checkbox" name=

问题 I have been making a script to display users and make changes to their admin privileges. Here is the code: while ($row= mysql_fetch_assoc($query)) { $uname= $row['username']; $fname= $row['first_name']; $lname= $row['last_name']; $email= $row['email']; $admin= $row['admin']; $insert .= '<tr> <td>' .$uname. '</td> <td>' .$fname. '</td> <td>' .$lname. '</td> <td>' .((isset($email)) ? $email:'No email set.'). '</td> <td>'.(($admin == 'y') ? 'Admin':'User').'</td> <td><input type="checkbox" name=

问题 I would like to concatenate data from two cells into one cell. I would also like to only combine those cells that have the same ID. Task ID Name 4355.2 Participant 4355.2 Leader 4462.1 Online 4462.1 Quick 4597.1 Slide 4597.1 One Page 4597.1 One Topic For example, for this, I would like a cell for 4355.2 with "Participant, Leader" as the data in that cell. The same type of data for 4462.1 with "Online and Quick" as the data for that cell. Task ID Name 4355.2 Participant, Leader Is there a way

问题 I am trying to do following in MATLAB, global a b c d e f g h l; A=[1 3;3 2]; B=[a 0;0 b]; C=[d 0;e f]; Ctranspose=transpose(C); D=[sqrt(d) 0;0 sqrt(f)]; E=Ctranspose/D; Etranspose=transpose(E); K=A+E; M=E*D*Etranspose; for a=1:10 for b=1:10 if K==M print(a); print(b); print(d); print(e); print(f); end end end I get following errors: a) Error using + Matrix dimensions must agree. Error in trial (line 6) K=A+B b) Error using vertcat CAT arguments dimensions are not consistent. Error in trial

问题 In PHP we can quickly concatenate strings: $a = "b"; $a .= "c"; which returns "bc" . How would we do this in Ruby? 回答1: irb(main):001:0> a = "ezcezc" => "ezcezc" irb(main):002:0> a << "erer" => "ezcezcerer" or irb(main):003:0> a += "epruneiruv" => "ezcezcererepruneiruv" 回答2: There are essentially two different ways: Concatenation in place with << (known as the "shovel"), this is equivalent to calling concat. Note that, like most operators in Ruby, << is a method call . str = "foo" str << "bar

问题 I have the following table Created Comment 2010/10/10 Text1 2010/11/11 Text2 2010/12/12 Text3 I need gather all comments into the single string SELECT @Comment = COALESCE(@Comment, '') + CHAR(13) + CHAR(10) + CONVERT(NVARCHAR(30), [dbo].[Comment].[Created], 101) + ': ' + ISNULL([Comment].[Text], '') FROM Comment Without ordering it works as expected end return all thee comments. But after running following code where ORDER BY clause is added: SELECT @Comment = COALESCE(@Comment, '') + CHAR(13

问题 I have the following table Created Comment 2010/10/10 Text1 2010/11/11 Text2 2010/12/12 Text3 I need gather all comments into the single string SELECT @Comment = COALESCE(@Comment, '') + CHAR(13) + CHAR(10) + CONVERT(NVARCHAR(30), [dbo].[Comment].[Created], 101) + ': ' + ISNULL([Comment].[Text], '') FROM Comment Without ordering it works as expected end return all thee comments. But after running following code where ORDER BY clause is added: SELECT @Comment = COALESCE(@Comment, '') + CHAR(13

问题 Please correct me if i'm wrong. In Java 8, for performance reasons, when concatenating several strings by the "+" operator StringBuffer was invoked. And the problem of creating a bunch of intermediate string objects and polluting the string pool was "resolved". What about Java 9? There'a new feature added as Invokedynamic. And a new class that resolves the problem even better, StringConcatFactory. String result = ""; List<String> list = Arrays.asList("a", "b", "c"); for (String n : list) {

问题 Let's say I have these assignments: points = [] point = (1, 2) How come when I do this: points += point It works completely fine, and gives me points = [1, 2]. However, If I do something like: points = points + point It gives me a TypeError: can only concatenate list (not "tuple") to list. Aren't these statements the same thing, though? 回答1: The difference, is that list += is equivalent to list.extend() , which takes any iterable and extends the list, it works as a tuple is an iterable. (And