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How can you determine how much disk space a particular MySQL table is taking up?
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For a table mydb.mytable run this for:
BYTES
SELECT (data_length+index_length) tablesize
FROM information_schema.tables
WHERE table_schema='mydb' and table_name='mytable';
KILOBYTES
SELECT (data_length+index_length)/power(1024,1) tablesize_kb
FROM information_schema.tables
WHERE table_s...
B-Tree vs Hash Table
In MySQL, an index type is a b-tree, and access an element in a b-tree is in logarithmic amortized time O(log(n)) .
5 Answ...
Creating a Pandas DataFrame from a Numpy array: How do I specify the index column and column headers
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You need to specify data, index and columns to DataFrame constructor, as in:
>>> pd.DataFrame(data=data[1:,1:], # values
... index=data[1:,0], # 1st column as index
... columns=data[0,1:]) # 1st row as the co...
When and why are database joins expensive?
... working set. Joins involving properly selected keys with correctly set up indexes are cheap, not expensive, because they allow significant pruning of the result before the rows are materialised.
Materialising the result involves bulk disk reads which are the most expensive aspect of the exercise ...
Random row selection in Pandas dataframe
...like this?
import random
def some(x, n):
return x.ix[random.sample(x.index, n)]
Note: As of Pandas v0.20.0, ix has been deprecated in favour of loc for label based indexing.
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improve ...
Remap values in pandas column with a dict
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map also works on an index where I couldn't figure out a way to do that with replace
– Max Ghenis
Mar 15 '19 at 16:42
1
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How to validate inputs dynamically created using ng-repeat, ng-show (angular)
...s the same name as the cell above and below it. I attempted to use the {{$index}} value to name the inputs, but despite the string literals in HTML appearing correct, it is now working.
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SQL - many-to-many table primary key
...r col1 and col2 values in the referenced tables are unique) and a separate index on (col2,col1) will catch those cases where the opposite order would execute faster. The surrogate is a waste of space.
You won't need indexes on the individual columns since the table should only ever be used to join ...
Pandas selecting by label sometimes return Series, sometimes returns DataFrame
In Pandas, when I select a label that only has one entry in the index I get back a Series, but when I select an entry that has more then one entry I get back a data frame.
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Why are joins bad when considering scalability?
...means smaller (and therefore faster) comparisons during the join operation
Indexes
Materialized/indexed views (think of this as a pre-computed join or managed de-normalization)
Computed columns. You can use this to hash or otherwise pre-compute the key columns of a join, such that what would be a co...