concat

Concatenate a list of pandas dataframes together

由 喜你入骨 提交于 2019-11-26 15:24:55
问题 I have a list of Pandas dataframes that I would like to combine into one Pandas dataframe. I am using Python 2.7.10 and Pandas 0.16.2 I created the list of dataframes from: import pandas as pd dfs = [] sqlall = "select * from mytable" for chunk in pd.read_sql_query(sqlall , cnxn, chunksize=10000): dfs.append(chunk) This returns a list of dataframes type(dfs[0]) Out[6]: pandas.core.frame.DataFrame type(dfs) Out[7]: list len(dfs) Out[8]: 408 Here is some sample data # sample dataframes d1 = pd

Difference(s) between merge() and concat() in pandas

由 二次信任 提交于 2019-11-26 15:12:33
问题 What's the essential difference(s) between pd.DataFrame.merge() and pd.concat() ? So far, this is what I found, please comment on how complete and accurate my understanding is: .merge() can only use columns (plus row-indices) and it is semantically suitable for database-style operations. .concat() can be used with either axis, using only indices, and gives the option for adding a hierarchical index. Incidentally, this allows for the following redundancy: both can combine two dataframes using

Why does Java's concat() method not do anything?

由 两盒软妹~` 提交于 2019-11-26 14:46:36
This code: String s = "TEST"; String s2 = s.trim(); s.concat("ING"); System.out.println("S = "+s); System.out.println("S2 = "+s2); results in this output: S = TEST S2 = TEST BUILD SUCCESSFUL (total time: 0 seconds) Why are "TEST" and "ING" not concatenated together? a String is immutable , meaning you cannot change a String in Java. concat() returns a new, concatenated, string. String s = "TEST"; String s2 = s.trim(); String s3 = s.concat("ING"); System.out.println("S = "+s); System.out.println("S2 = "+s2); System.out.println("S3 = "+s3); Because String is immutable - class String does not

String concatenation in MySQL

由 好久不见. 提交于 2019-11-26 12:21:28
I am using MySQL and MySQL Workbench 5.2 CE. When I try to concatenate 2 columns, last_name and first_name , it doesn't work : select first_name + last_name as "Name" from test.student MySQL is different from most DBMSs use of + or || for concatenation. It uses the CONCAT function: SELECT CONCAT(first_name, " ", last_name) AS Name FROM test.student As @eggyal pointed out in comments, you can enable string concatenation with the || operator in MySQL by setting the PIPES_AS_CONCAT SQL mode. Try: select concat(first_name,last_name) as "Name" from test.student or, better: select concat(first_name,

MySQL CONCAT returns NULL if any field contain NULL

由 泪湿孤枕 提交于 2019-11-26 12:09:34
问题 I have following data in my table \"devices\" affiliate_name affiliate_location model ip os_type os_version cs1 inter Dell 10.125.103.25 Linux Fedora cs2 inter Dell 10.125.103.26 Linux Fedora cs3 inter Dell 10.125.103.27 NULL NULL cs4 inter Dell 10.125.103.28 NULL NULL I executed below query SELECT CONCAT(`affiliate_name`,\'-\',`model`,\'-\',`ip`,\'-\',`os_type`,\'-\',`os_version`) AS device_name FROM devices It returns result given below cs1-Dell-10.125.103.25-Linux-Fedora cs2-Dell-10.125

Concatenate strings in Less

由 不羁岁月 提交于 2019-11-26 12:08:01
问题 I think this is not possible, but I thought I ask in case there is a way. The idea is that I have a variable for path to web resource folder: @root: \"../img/\"; @file: \"test.css\"; @url: @root@file; .px { background-image: url(@url); } I get this as a result: .px { background-image: url(\"../img/\" \"test.css\"); } But, I want the strings to combine into one string like this: .px { background-image: url(\"../img/test.css\"); } Is it possible to concatenate strings together in Less? 回答1: Use

MySQL concat() to create column names to be used in a query?

由 会有一股神秘感。 提交于 2019-11-26 11:12:05
问题 I would like to concatenate column names in a way that the first part of the column name is a string and the second part is a number which is the result of another query. For example: SELECT CONCAT(\'column\', mytable.mycolumn) FROM table ... Can this be done in some way. This way it doesn\'t give me errors but I don\'t get the expected result and it seems the concatenation doesn\'t work. 回答1: I previously said that this couldn't be done, but I was wrong. I ended up needing something like

JavaScript NodeList

由 爷，独闯天下 提交于 2019-11-26 08:25:25
问题 is there a way to join 2 NodeLists returned by 2 calls of document.getElementsByTagName? Say, I have the following code var inputs = documentElement.getElementsByTagName(\'input\'); var selects = document.getElementsByTagName(\'select\'); I want to loop through the results. Is it possible in one loop? Thank you in advance! 回答1: Seems like you can use the same Array.prototype.slice.call that makes the args array-like object become an array. (See here) var inputs = document.getElementsByTagName

How do I concatenate strings in Swift?

由 狂风中的少年 提交于 2019-11-26 07:59:14
问题 How to concatenate string in Swift? In Objective-C we do like NSString *string = @\"Swift\"; NSString *resultStr = [string stringByAppendingString:@\" is a new Programming Language\"]; or NSString *resultStr=[NSString stringWithFormat:@\"%@ is a new Programming Language\",string]; But I want to do this in Swift-language. 回答1: You can concatenate strings a number of ways: let a = "Hello" let b = "World" let first = a + ", " + b let second = "\(a), \(b)" You could also do: var c = "Hello" c +=

Merge (Concat) Multiple JSONObjects in Java

由 China☆狼群 提交于 2019-11-26 05:27:38
问题 I am consuming some JSON from two different sources, I end up with two JSONObject s and I\'d like to combine them into one. Data: \"Object1\": { \"Stringkey\":\"StringVal\", \"ArrayKey\": [Data0, Data1] } \"Object2\": { \"Stringkey\":\"StringVal\", \"Stringkey\":\"StringVal\", \"Stringkey\":\"StringVal\", } Code, using http://json.org/java/ library: // jso1 and jso2 are some JSONObjects already instantiated JSONObject Obj1 = (JSONObject) jso.get(\"Object1\"); JSONObject Obj2 = (JSONObject)
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