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Shell Programming and Scripting
Matrix to 3 col sorted
Post 303003886 by ctsgnb on Friday 22nd of September 2017 06:08:49 AM
09-22-2017
Whatever strategy you choose, according to your expectation, you will get an output file that is near 5 times bigger than your input file.
input file :
rows = 400k
columns = 3000
Total amount of datas = 400k x 3000 = 1,2 billions
output file :
rows = (400k -1) x ( 3000 -3 )
"-1" because of the header row
"-3" because the 3 first contains the datas you want
columns = 5 (i take into account the datas, not the formatting and "__" stuff)
Total amount of datas = 5 x (400k -1) x ( 3000 -3 ) = 5,99...billions
Indeed, since you will be repeating the datas of the first 3 column for each and every subsequent column. (so (3 + 2 ) x (3000 - 3) ) rather than having it once for all of them ( "+ 2" is because you even want to add the header and the values of the subsequent column).
So just because of your prerequisits and expectations, for sure you will have to write more data, and thus you will need the corresponding number of I/O writing, independently of the strategy you choose.
If you have a huge amount of data to write, then there is and uncompressible amount of time to do it.
Of course I/O operations are quicker to do in RAM or SSD than on a standard hard drive, but still ...
It would be cheaper to save the transposed matrix and request on it
So you will have it twice : in line and in columns ... of course it will cost you 1,2 billions of datas more.
But 1,2 billions x 2 = 2,4 billions is still more than twice smaller than 5,9 billions of datas !
Anyway, processing such an amount of data using files is inappropriate : this is what Database have been designed for...
My 2 cents ...
PS// The reality might even be worse since i didn't even take into account the size of the datas, just the number of them ...
input file :
rows = 400k
columns = 3000
Total amount of datas = 400k x 3000 = 1,2 billions
output file :
rows = (400k -1) x ( 3000 -3 )
"-1" because of the header row
"-3" because the 3 first contains the datas you want
columns = 5 (i take into account the datas, not the formatting and "__" stuff)
Total amount of datas = 5 x (400k -1) x ( 3000 -3 ) = 5,99...billions
Indeed, since you will be repeating the datas of the first 3 column for each and every subsequent column. (so (3 + 2 ) x (3000 - 3) ) rather than having it once for all of them ( "+ 2" is because you even want to add the header and the values of the subsequent column).
So just because of your prerequisits and expectations, for sure you will have to write more data, and thus you will need the corresponding number of I/O writing, independently of the strategy you choose.
If you have a huge amount of data to write, then there is and uncompressible amount of time to do it.
Of course I/O operations are quicker to do in RAM or SSD than on a standard hard drive, but still ...
It would be cheaper to save the transposed matrix and request on it
So you will have it twice : in line and in columns ... of course it will cost you 1,2 billions of datas more.
But 1,2 billions x 2 = 2,4 billions is still more than twice smaller than 5,9 billions of datas !
Anyway, processing such an amount of data using files is inappropriate : this is what Database have been designed for...
My 2 cents ...
PS// The reality might even be worse since i didn't even take into account the size of the datas, just the number of them ...
Last edited by ctsgnb; 09-22-2017 at 12:18 PM..
This User Gave Thanks to ctsgnb For This Post:
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LEARN ABOUT REDHAT
spottopgm
spottopgm(1L) spottopgm(1L) NAME
spottopgm - convert SPOT satellite images to Portable Greymap format SYNTAX
spottopgm [-1|2|3] [Firstcol Firstline Lastcol Lastline] inputfile OPTIONS
-1|2|3 Extract the given colour from the SPOT image. The colours are infra-red, visible light and ultra-violet, although I don't know which corresponds to which number. If the image is in colour, this will be announced on standard error. The default colour is 1. Firstcol Firstline Lastcol Lastline Extract the specified rectangle from the SPOT image. Most SPOT images are 3000 lines long and 3000 or more columns wide. Unfortu- nately the SPOT format only gives the width and not the length. The width is printed on standard error. The default rectangle is the width of the input image by 3000 lines. DESCRIPTION
Spottopgm converts the named inputfile into Portable Greymap format, defaulting to the first color and the whole SPOT image unless speci- fied by the options. INSTALLATION
You must edit the source program and either define BIG_ENDIAN or LITTLE_ENDIAN, and fix the typedefs for uint32_t, uint16_t and uint8_t appropriately. BUGS
Currently spottopgm doesn't determine the length of the input file; this would involve two passes over the input file. It defaults to 3000 lines instead. Spottopgm could extract a three-color image (ppm), but I didn't feel like making the program more complicated than it is now. Besides, there is no one-to-one correspondence between red, green, blue and infra-red, visible and ultra-violet. I've only had a limited number of SPOT images to play with, and therefore wouldn't guarantee that this will work on any other images. AUTHOR
Warren Toomey wkt@csadfa.cs.adfa.oz.au SEE ALSO
The rest of the Pbmplus suite. spottopgm(1L)