To transpose an array, NumPy just swaps the shape and stride information for each axis. Here are the strides: >>> arr.strides (64, 32, 8) >>> arr.transpose(1, 0, 2).strides (32, 64, 8) Notice that the transpose operation swapped the strides for axis 0 and axis 1. The lengths of these axes were also swapped (both lengths … Read more
Use crosstab() from the tablefunc module. SELECT * FROM crosstab( $$SELECT user_id, user_name, rn, email_address FROM ( SELECT u.user_id, u.user_name, e.email_address , row_number() OVER (PARTITION BY u.user_id ORDER BY e.creation_date DESC NULLS LAST) AS rn FROM usr u LEFT JOIN email_tbl e USING (user_id) ) sub WHERE rn < 4 ORDER BY user_id $$ , … Read more
This is a good question. There are many reason you would want to actually transpose the matrix in memory rather than just swap coordinates, e.g. in matrix multiplication and Gaussian smearing. First let me list one of the functions I use for the transpose (EDIT: please see the end of my answer where I found … Read more
It is relatively simple to do with basic Spark SQL functions. Python from pyspark.sql.functions import array, col, explode, struct, lit df = sc.parallelize([(1, 0.0, 0.6), (1, 0.6, 0.7)]).toDF([“A”, “col_1”, “col_2”]) def to_long(df, by): # Filter dtypes and split into column names and type description cols, dtypes = zip(*((c, t) for (c, t) in df.dtypes if … Read more
You can use pivot_table: pd.pivot_table(df, values=”Value”, index=[‘Country’,’Year’], columns=”Indicator”).reset_index() this outputs: Indicator Country Year 1 2 3 4 5 0 Angola 2005 6 13 10 11 5 1 Angola 2006 3 2 7 3 6
Yes you can perform a dynamic pivot. Sometimes it is easier to work up the PIVOT query using a static version first so you can see how the query and results will appear. Then transform the query into a dynamic version. Here is an example of a static vs. dynamic version of a query: Static … Read more
It’s working exactly as it’s supposed to. The transpose of a 1D array is still a 1D array! (If you’re used to matlab, it fundamentally doesn’t have a concept of a 1D array. Matlab’s “1D” arrays are 2D.) If you want to turn your 1D vector into a 2D array and then transpose it, just … Read more
An efficient way to transpose a file in Bash
output = array[0].map((_, colIndex) => array.map(row => row[colIndex])); map calls a provided callback function once for each element in an array, in order, and constructs a new array from the results. callback is invoked only for indexes of the array which have assigned values; it is not invoked for indexes which have been deleted or … Read more
zip is its own inverse! Provided you use the special * operator. >>> zip(*[(‘a’, 1), (‘b’, 2), (‘c’, 3), (‘d’, 4)]) [(‘a’, ‘b’, ‘c’, ‘d’), (1, 2, 3, 4)] The way this works is by calling zip with the arguments: zip((‘a’, 1), (‘b’, 2), (‘c’, 3), (‘d’, 4)) … except the arguments are passed to … Read more