multiple colons in makefiles

more than one colon in gnu make makefile rule

gnu make makefiles more than one colon

i could not find the following page while googling for the search queries mentioned above. hope google is able to send people to this page at which point they will find what they are looking for

https://www.gnu.org/software/make/manual/html_node/Static-Usage.html#Static-Usage

default user agent in scrapy

scrapy settings --get=USER_AGENT

Scrapy/1.2.1 (+http://scrapy.org)

scikit-learn NLP list english stopwords

from sklearn.feature_extraction import stop_words

print(stop_words.ENGLISH_STOP_WORDS)

currently there are 318 words in that frozenset.

NLTK also has its own stopwords

from nltk.corpus import stopwords
print(stopwords.words('english'))

there are 153 words in that

apache hive divide a column by its sum

select a/sum(a) from foo; -- WRONG!

will not work because sum(a) would work on each row and will return the number present in that row resulting in all 1. since sum(n) = n where n is a single number.

here is where we can make good use of  hive windowing and analytics functions.

the solution is to use the following:

select a/sum(a) over () from foo; -- RIGHT !!!

here we are instructing that the sum be performed over the entire column ‘a’.

you could of course make 2 queries and calculate the sum of a first and then hardcode the sum in another query but that means you are performing 2 passes over the table for sure. now i can’t be sure how many passes over the table are being made in the right query above. if you know the answer please post in the comments below.

archlinux how to install from AUR

It has been a while since I played with Archlinux. Meanwhile AUR has transitioned and now uses version controlled PKGBUILDs. So here is how to go about it.

Let us take the example of the package cower.

If you visit that page you will find a “Download snapshot” link under the Package Actions box to the right of the page near the top of the page. Just click on it and you will download a compressed tarball; cower.tar.gz in this case. Uncompress that to find the actual PKGBUILD in it. I also noticed a hidden file called .SRCINFO in the same folder. Now you can simply issue the command “makepkg -irs” in the same directory and you are all set.

The other way is to git clone the repo. The repo link is right at the top of the page under Git Clone URL. If you clone the repo you will find the PKGBUILD and .SRCINFO and .git directory in there. Again use “makepkg -irs” to install the package.

make apache hive silent from inside the shell

If one launches Hive using the “-S” or “–silent” option then Hive does not print progress information. However if you are already inside the Hive command line shell then you can control this behaviour by setting the value of silent.

set silent=on; -- make hive silent

set silent=false; -- make hive print progress information

 

apache hive windowing functions lag and lead

window functions allow one to look at the previous values or next values of a column. for example if i want to subtract the previous row value from the current row value then window functions lag and lead can be used.

let us take up an example.

first create a text file containing numbers 1 through 9 with a single number on each line like so

1

2

3

.

.

9

call the file data.txt.

next we create a table in hive.

create table foo (a int);

next we load our data.txt file in to this created table using the following

load data local inpath 'data.txt' overwrite into table foo;

we want to access previous and next values over column ‘a’ note therefore the over clause in the following query

select lag(a, 1) over (order by a) as previous, a, lead(a, 1) over (order by a) as next from foo;

which outputs the following:

previous a next
NULL 1 2
1 2 3
2 3 4
3 4 5
4 5 6
5 6 7
6 7 8
7 8 9
8 9 NULL

note how the previous and next values are NULL at the edge cases. You could specify a value in such cases as in the following query which specifies 0.

select lag(a, 1, 0) over (order by a) as previous, a, lead(a, 1, 0) over (order by a) as next from foo;

which outputs the following:

previous a next
0 1 2
1 2 3
2 3 4
3 4 5
4 5 6
5 6 7
6 7 8
7 8 9
8 9 0

lag(a, 1) will fetch the previous value while lag(a, 2) will fetch the previous to previous value.