Archive: July 2020

Clojure Goodness: Taking Or Dropping Elements From A Collection Based On Predicate

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Hubert Klein Ikkink

In Clojure we can take or drop elements from a collection based on a predicate using the functions take-while and drop-while. With the function take-while we take elements as long as the predicate returns true. Once the predicate returns false the function stops returning elements. Using the function drop-while we skip elements in the collection if the predicate returns true. If the predicate returns false the remaining elements in the collection are returned.

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Clojure Goodness: Turn Java Object To Map With bean Function

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Hubert Klein Ikkink

The map data structure is used a lot in Clojure. When we want to use Java objects in our Clojure code we can convert the Java object to a map with the bean function. This function will use reflection to get all the properties of the Java object and converts each property with the property value to a key with value in the resulting map. The bean function will not recursively convert nested objects to a map, only the top-level properties are turned into key value pairs.

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Clojure Goodness: Create And Initialize Object Based On Java Class With doto

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Hubert Klein Ikkink

It is very easy to work with Java classes in Clojure. If we want to create a new object based on a Java class and invoke methods to initialize the object directly we can use the doto macro. The first argument is an expression to create a new object and the rest of the arguments are functions to invoke methods on the newly created object. The object returned from the first argument is passed as first argument to the method invocations. The doto function returns the object that is created with the first argument.

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Clojure Goodness: Replacing Characters In A String With escape Function

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Hubert Klein Ikkink

The clojure.string namespace contains a lot of useful functions to work with string values. The escape function can be used to replace characters in a string with another character. The function accepts as first argument the string value and the second argument is a map. The map has characters as key that need to be replaced followed by the value it is replaced with. For example the map {\a 1 \b 2} replaces the character a with 1 and the character b with 2.

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Clojure Goodness: Concatenation Of Map Function Results With mapcat

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Hubert Klein Ikkink

When we use a function as argument for the map function that returns a collection we would get nested collections. If we want to turn the result into a single collection we can concatenate the elements from the collections by applying the concat function, but we can do this directly with the function mapcat. The function mapcat takes as first argument a function (that returns a collection) and one or more collections as next arguments.

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Clojure Goodness: Creating Union Of Sets

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Hubert Klein Ikkink

When we are working with sets in Clojure we can use some useful functions from the clojure.set namespace. In a previous post we learned how we can get the difference of several sets. To get the union of several input sets we use the union function of the clojure.set namespace. The function returns a new set that is the union of unique elements from the input sets. A nil value is ignored by the union function.

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Clojure Goodness: Keyword As Function

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Hubert Klein Ikkink

In Clojure functions are everywhere. In a previous post we learned that sets can be functions, but Clojure also makes keywords functions. A keyword is a symbol starting with a colon (:) and is mostly used in map entries as key symbol. The keyword as function accepts a map as single argument and returns the value for the key that equals the keyword in the map or nil if the keyword cannot be found.

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