dictionary

java的Map

由 和自甴很熟 提交于 2021-02-13 16:31:33
HashMap HashMap和Hashtable区别 Hashtable的方法是同步的，HashMap未经同步，所以在多线程场合要手动同步HashMap,这如同Vector和ArrayList一样。 Hashtable不允许null值(key和value都不可以)，HashMap允许null值(key和value都可以)。 两者的遍历方式大同小异，Hashtable仅仅比HashMap多一个elements方法，两者都能通过values()方法返回一个Collection，然后进行遍历，两者也可以通过entrySet()返回一个Set，然后进行遍历处理。 Hashtable使用Enumeration, HashMap使用Iterator。 哈希值的使用不同，Hashtable直接使用对象的hashCode，而HashMap重新计算hash值，而且用于代替求模。 Hashtable的hash数组默认大小是11，增加的方式是old * 2 + 1；HashMap的hash数组默认大小是16，而且一定是2的指数。 Hashtable基于Dictionary类，而HashMap基于AbstractMap类。 HashMap中的key可以是任何对象或数据类型吗 可以为null，但不能是可变对象，如果是可变对象的话，对象中的属性改变时，则相应的对象hashCode也进行相应改变

动态拼接Lambda表达式

由 六月ゝ 毕业季﹏ 提交于 2021-02-13 08:14:14
添加类 public class ParameterRebinder : ExpressionVisitor { private readonly Dictionary<ParameterExpression, ParameterExpression> map; public ParameterRebinder(Dictionary<ParameterExpression, ParameterExpression> map) { this .map = map ?? new Dictionary<ParameterExpression, ParameterExpression> (); } public static Expression ReplaceParameters(Dictionary<ParameterExpression, ParameterExpression> map, Expression exp) { return new ParameterRebinder(map).Visit(exp); } protected override Expression VisitParameter(ParameterExpression p) { ParameterExpression replacement; if (map.TryGetValue(p, out

Sort dictionary of dictionaries by value Python ( 3 Level Dict ) [closed]

由 天大地大妈咪最大 提交于 2021-02-11 18:05:26
问题 Closed . This question needs to be more focused. It is not currently accepting answers. Want to improve this question? Update the question so it focuses on one problem only by editing this post. Closed 5 years ago . Improve this question I have a dict like this: { 'INT-ABC1': { 'acc1': {'val': -22313.7381693064, 'Qua': -241.0}, 'acc2': {'val': -1312.940854148, 'Qua': -13.0} }, 'INT-ABC2': { 'acc1': {'val': -131.2510359399, 'Qua' : -23.0}, 'acc3': {'val': -131.40521409002, 'Qua' : -13.0},

ES6 Sum by object property in an array

由 旧街凉风 提交于 2021-02-11 17:40:52
问题 I am trying to sum the unit value by date, and create a new array where there are no duplicate dates. For example, I want to calculate the total of 2015-12-04 00:01:00 . This date has occurred 2 times in the following data, its value is 5 and 6 , which is going to be: [{date: '2015-12-04 00:01:00', unit: 11}, ... etc] I have tried arr = results.map(x => x.unit).reduce((a,c) => a + c) but it only return a single value, not an array. results = [ { unit: 5, date: '2015-12-04 00:01:00' }, { unit:

ES6 Sum by object property in an array

由 蹲街弑〆低调 提交于 2021-02-11 17:39:43
问题 I am trying to sum the unit value by date, and create a new array where there are no duplicate dates. For example, I want to calculate the total of 2015-12-04 00:01:00 . This date has occurred 2 times in the following data, its value is 5 and 6 , which is going to be: [{date: '2015-12-04 00:01:00', unit: 11}, ... etc] I have tried arr = results.map(x => x.unit).reduce((a,c) => a + c) but it only return a single value, not an array. results = [ { unit: 5, date: '2015-12-04 00:01:00' }, { unit:

Converting dataframe to dictionary in pyspark without using pandas

由 大城市里の小女人 提交于 2021-02-11 16:55:20
问题 Following up this question and dataframes, I am trying to convert a dataframe into a dictionary. In pandas I was using this: dictionary = df_2.unstack().to_dict(orient='index') However, I need to convert this code to pyspark. Can anyone help me with this? As I understand from previous questions such as this I would indeed need to use pandas, but the dataframe is way too big for me to be able to do this. How can I solve this? EDIT: I have now tried the following approach: dictionary_list = map

Converting dataframe to dictionary in pyspark without using pandas

由 …衆ロ難τιáo~ 提交于 2021-02-11 16:54:15
问题 Following up this question and dataframes, I am trying to convert a dataframe into a dictionary. In pandas I was using this: dictionary = df_2.unstack().to_dict(orient='index') However, I need to convert this code to pyspark. Can anyone help me with this? As I understand from previous questions such as this I would indeed need to use pandas, but the dataframe is way too big for me to be able to do this. How can I solve this? EDIT: I have now tried the following approach: dictionary_list = map

SnakeYaml get stacked keys

由 淺唱寂寞╮ 提交于 2021-02-11 16:51:26
问题 When this is my .yml file: test1: "string1" test2: test3: "string2" How do I get the value of test3 ? Map<String, Object> yamlFile = new Yaml().load(YamlFileInputStream); yamlFile.get("test1"); // output: string1 yamlFile.get("test2"); // output: {test3=string2} yamlFile.get("test2.test3"); // output: key not found 回答1: YAML does not have „stacked keys“ . It has nested mappings. The dot . is not a special character and can occur normally in a key, therefore you cannot use it for querying

Find a value from a dictionary in python by taking a key from user input [closed]

由 我是研究僧i 提交于 2021-02-11 15:51:01
问题 Closed . This question needs to be more focused. It is not currently accepting answers. Want to improve this question? Update the question so it focuses on one problem only by editing this post. Closed 1 year ago . Improve this question I have a dictionary. How can I get the value by taking the key from user? d = {'a': '1', 'b': '2', 'c':'3'} If the user enters a I wanted to print value '1' . 回答1: This will do for you: print(p["a"]) This prints the number for "a" in the dictionary. For your

Find a value from a dictionary in python by taking a key from user input [closed]

由 大兔子大兔子 提交于 2021-02-11 15:50:53
问题 Closed . This question needs to be more focused. It is not currently accepting answers. Want to improve this question? Update the question so it focuses on one problem only by editing this post. Closed 1 year ago . Improve this question I have a dictionary. How can I get the value by taking the key from user? d = {'a': '1', 'b': '2', 'c':'3'} If the user enters a I wanted to print value '1' . 回答1: This will do for you: print(p["a"]) This prints the number for "a" in the dictionary. For your
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