[SciPy-User] find intervall in array

Massimo Di Stefano massimodisasha@yahoo...
Tue Jan 26 04:15:10 CST 2010


Hi All,

i have a 2xN array where : 

- first column = integer values sorted from min to max
- second column = float values (range 0 - 1)

an example array can look like :

from numpy import zeros, array
import random
a = zeros((100,2),float)
for i in range(100):
  a[i,0] = random.randrange(1000,2000,10)
  a[i,1] = random.random()



the first column represent "Z" (elevation values)
the second column represent percentage 0 = 0% , 1 = 100% (pixel % coverage in a map at given Z)

i need to detect the Z value correspond to a precise percentage (25%, 50%, 75%)

he Z value i need to find is deducted from a formula like :

z = z1 + ((z2 - z1) / (f2 - f1)) * (f - f1)

where :

f  = precise percentage (know value) -> (0.25, 0.50, 0.75)  [this value can be not present in the a[i,1] array]

f1, f2 =  are the a[i,1] values near the " f " value   where     [ f1 <= f <= f2 ]
z1, z2 =  Z value correspond to the f1, f2

as example :

array a =

z           f
1234    0.03
1345    0.58
1456    0.24
1457    0.63
1458    0.41
1459    0.78
1365    0.7
1468    0.56
1545    0.54

if   
f = 0.5 :
z = 1545 + ((1468 - 1545) / (0.56 - 0.54)) * (0.5 - 0.54)

any suggestion on how can i find "f1 , f2" ?


thanks!!!

Massimo.


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