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  2. Wide and narrow data - Wikipedia

    en.wikipedia.org/wiki/Wide_and_narrow_data

    The pandas package in Python implements this operation as "melt" function which converts a wide table to a narrow one. The process of converting a narrow table to wide table is generally referred to as "pivoting" in the context of data transformations.

  3. Round-off error - Wikipedia

    en.wikipedia.org/wiki/Round-off_error

    There are two common rounding rules, round-by-chop and round-to-nearest. The IEEE standard uses round-to-nearest. Round-by-chop: The base-expansion of is truncated after the ()-th digit. This rounding rule is biased because it always moves the result toward zero.

  4. Data orientation - Wikipedia

    en.wikipedia.org/wiki/Data_orientation

    The two most common representations are column-oriented (columnar format) and row-oriented (row format). [ 1 ] [ 2 ] The choice of data orientation is a trade-off and an architectural decision in databases , query engines, and numerical simulations. [ 1 ]

  5. Hash table - Wikipedia

    en.wikipedia.org/wiki/Hash_table

    The distribution needs to be uniform only for table sizes that occur in the application. In particular, if one uses dynamic resizing with exact doubling and halving of the table size, then the hash function needs to be uniform only when the size is a power of two. Here the index can be computed as some range of bits of the hash function.

  6. Quartile - Wikipedia

    en.wikipedia.org/wiki/Quartile

    Use the median to divide the ordered data set into two halves. The median becomes the second quartile. If there are an odd number of data points in the original ordered data set, do not include the median (the central value in the ordered list) in either half.

  7. Sparse dictionary learning - Wikipedia

    en.wikipedia.org/wiki/Sparse_dictionary_learning

    Sparse dictionary learning (also known as sparse coding or SDL) is a representation learning method which aims to find a sparse representation of the input data in the form of a linear combination of basic elements as well as those basic elements themselves. These elements are called atoms, and they compose a dictionary.

  8. Mean squared error - Wikipedia

    en.wikipedia.org/wiki/Mean_squared_error

    The MSE is the second moment (about the origin) of the error, and thus incorporates both the variance of the estimator (how widely spread the estimates are from one data sample to another) and its bias (how far off the average estimated value is from the true value). [citation needed] For an unbiased estimator, the MSE is the variance of the ...

  9. Bessel's correction - Wikipedia

    en.wikipedia.org/wiki/Bessel's_correction

    The following statements explain the meaning of the remaining columns: The sum of the entries in the first column (a 2) is the sum of the squares of the distance from sample to sample mean; The sum of the entries in the last column (b 2) is the sum of squared distances between the measured sample mean and the correct population mean