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I am working with a dataset that has users as Strings (ie. B000GKXY4S). I would like to convert each of these users to int, so I can use Rating(user: Int, product: Int, rating: Double) class in Apache Spark ALS. What is the most efficient way to do this? Preferably using Spark Scala functions or python native functions.
If you just want any matchable String to an int - String.hashCode(). However you will have to deal with possible hash collisions. Alternatively you'd have to convert each character to its int value and append (not add) all of these together.
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I have an encoded string stored in my DB that kinda looks like this (altered for confidentiality):
\x7b22747c
How do I decode this string? (Using either Java or Python)
There is code elsewhere that used tobytes() function to decode it. But I don't own the code so I am not sure what it's doing.
The comments helped in looking in the right place.
Here is what worked for me:
bytes.fromhex('7b22747').decode()
So I just had to remove the \x and then just decode the remaining string which was an encoded hex string.
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Calculate the sum of amountField in MyDTO, Java 8
private Double getSum(List<MyDTO> myDTOList) {
return myDTOList.stream().map(MyDTO::getAmount).reduce(0d, Double::sum);
}
You can use Stream.mapToDouble to convert it into a DoubleStream and then use DoubleStream.sum:
return myDTOList.stream().mapToDouble(MyDTO::getAmount).sum();
To mention, the above shall work for amount being of integer type as well, while the code shared by you and this shall still work fine if the type of amount is already double.
Or as pointed out in comments by you, if your DTO object can be null, you can filter out those values using:
return myDTOList.stream().filter(Objects::nonNull).mapToDouble(MyDTO::getAmount).sum();
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I want to know where is the difference between System.out.write and System.out.print in my Java class.
The two methods of PrintStream have different meanings:
print(int) writes a decimal representation of the entire int, while
write(int) writes the least significant byte of the specified int to the output.
This leads to different results: if you call print(48), the output is going to be 48, but if you call write(48), the output would be system-dependent, but on most systems it would be 0.
Demo.
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I am developing a Java program and I'm meeting cases where I get undecided whether to use the casting a string to integer method, or to use the integer.parseInt method. Is there any clear benefit for either of the two methods?
With 'casting to string method', I mean:
String.valueOf(integer);
As far as I know, it's not possible to cast from a String to an int, so using Integer.parseInt seems like the best option here.
Looking at your edits about using valueOf, perhaps this link may help: Integer.valueOf() vs. Integer.parseInt()
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Why do most programmers avoid using the float and long data types in their video tutorials?
Is it only to avoid the "0000f" and "0000L" notation?
I avoid float has it has poor precision. I would rather use double (or long with fixed precision or if I have to BigDecimal).
I suspect long is not often used as int is usually enough and many Java APIs only accept int values. e.g. array sizes and Collection/Map size() must be int.
And why should they use them? Perhaps the one reason is to avoid writing a letter indicating that the float/long type is used.
However if you don't need any special precision, why use double instead of float or long instead of int?