cl.interp throwing "IndexError: list index out of range"

[spalaciob]

Trying to use cl.interp function. It throws an IndexError depending on the length of the new color list.
Steps to reproduce:

>>> colors = ['rgb(27,158,119)',
 'rgb(217,95,2)',
 'rgb(117,112,179)',
 'rgb(231,41,138)',
 'rgb(102,166,30)',
 'rgb(230,171,2)',
 'rgb(166,118,29)']
>>> works = cl.interp(colors, 10)
>>> fails = cl.interp(colors, 11)
/usr/local/lib/python2.7/dist-packages/colorlover/__init__.pyc in interp(scl, r)
   1821         c_i = int(i*math.floor(SCL_FI)/round(r[-1])) # start color index
   1822         hsl_o = rgb_to_hsl( scl[c_i] ) # convert rgb to hls
-> 1823         hsl_f = rgb_to_hsl( scl[c_i+1] )
   1824         section_min = c_i*r[-1]/SCL_FI
   1825         section_max = (c_i+1)*(r[-1]/SCL_FI)

IndexError: list index out of range

The problem is that c_i can round to len(scl)-1 depending on the length of r, hence scl[c_i+1] will end up being out of bounds. A naive solution would imply checking for that specific corner case (I'm sure there's a more elegant way though).

[garyfeng]

+1. The following gives the same error message as above, but n=28 works.

colorList = cl.to_hsl( cl.interp( cl.scales['11']['div']['RdYlBu'], 21) ) 

[garyfeng]

Quick fix, as suggested by @spalaciob

    for i in r:
        # garyfeng: c_i could be rounded up so scl[c_i+1] will go off range
        #c_i = int(i*math.floor(SCL_FI)/round(r[-1])) # start color index
        c_i = int(math.floor(i*math.floor(SCL_FI)/round(r[-1]))) # start color index
        hsl_o = rgb_to_hsl( scl[c_i] ) # convert rgb to hls
        hsl_f = rgb_to_hsl( scl[c_i+1] ) if c_i < len(scl)-1 else hsl_o
        section_min = c_i*r[-1]/SCL_FI
        section_max = (c_i+1)*(r[-1]/SCL_FI)
        fraction = (i-section_min)/(section_max-section_min)
        hsl = interp3( fraction, hsl_o, hsl_f )
        c.append( 'hsl'+str(hsl) )

[garyfeng]

Forget the above code. It masks #6 and doesn't fix #7. The math is not right.

This is much better, fixing both #6 and #7, although some of the color interpolation is odd. Here we show the math, where we wish to map len(scl)- intervals to r-1 intervals. We want to make sure c_i never goes out of bound.

scl = cl.scales['3']['div']['RdYlBu']
SCL_FI = len(scl)-1
r=25
r = [x*1.0*SCL_FI/r for x in range(r)] if isinstance( r, int ) else r
for i in r:
    c_i = int(math.floor(i))
    section_min = math.floor(i)
    section_max = math.ceil(i)
    fraction = (i-section_min) #/(section_max-section_min)

    print (i, c_i, section_min, section_max, fraction) 

which gives:

(0.0, 0, 0.0, 0.0, 0.0)
(0.08, 0, 0.0, 1.0, 0.08)
(0.16, 0, 0.0, 1.0, 0.16)
(0.24, 0, 0.0, 1.0, 0.24)
(0.32, 0, 0.0, 1.0, 0.32)
(0.4, 0, 0.0, 1.0, 0.4)
(0.48, 0, 0.0, 1.0, 0.48)
(0.56, 0, 0.0, 1.0, 0.56)
(0.64, 0, 0.0, 1.0, 0.64)
(0.72, 0, 0.0, 1.0, 0.72)
(0.8, 0, 0.0, 1.0, 0.8)
(0.88, 0, 0.0, 1.0, 0.88)
(0.96, 0, 0.0, 1.0, 0.96)
(1.04, 1, 1.0, 2.0, 0.040000000000000036)
(1.12, 1, 1.0, 2.0, 0.1200000000000001)
(1.2, 1, 1.0, 2.0, 0.19999999999999996)
(1.28, 1, 1.0, 2.0, 0.28)
(1.36, 1, 1.0, 2.0, 0.3600000000000001)
(1.44, 1, 1.0, 2.0, 0.43999999999999995)
(1.52, 1, 1.0, 2.0, 0.52)
(1.6, 1, 1.0, 2.0, 0.6000000000000001)
(1.68, 1, 1.0, 2.0, 0.6799999999999999)
(1.76, 1, 1.0, 2.0, 0.76)
(1.84, 1, 1.0, 2.0, 0.8400000000000001)
(1.92, 1, 1.0, 2.0, 0.9199999999999999)

The corresponding code to replace interp():

def interp(scl, r):
    ''' Interpolate a color scale "scl" to a new one with length "r"
        Fun usage in IPython notebook:
        HTML( to_html( to_hsl( interp( cl.scales['11']['qual']['Paired'], 5000 ) ) ) ) '''
    c = []
    SCL_FI = len(scl)-1 # final index of color scale
    # garyfeng:
    # the following line is buggy.
    # r = [x * 0.1 for x in range(r)] if isinstance( r, int ) else r
    r = [x*1.0*SCL_FI/r for x in range(r)] if isinstance( r, int ) else r
    # end garyfeng

    scl = to_numeric( scl )

    def interp3(fraction, start, end):
        ''' Interpolate between values of 2, 3-member tuples '''
        def intp(f, s, e):
            return s + (e - s)*f
        return tuple([intp(fraction, start[i], end[i]) for i in range(3)])

    def rgb_to_hsl(rgb):
        ''' Adapted from M Bostock's RGB to HSL converter in d3.js
            https://github.com/mbostock/d3/blob/master/src/color/rgb.js '''
        r,g,b = float(rgb[0])/255.0,\
                float(rgb[1])/255.0,\
                float(rgb[2])/255.0
        mx = max(r, g, b)
        mn = min(r, g, b)
        h = s = l = (mx + mn) / 2
        if mx == mn: # achromatic
            h = 0
            s = 0 if l > 0 and l < 1 else h
        else:
            d = mx - mn;
            s =  d / (mx + mn) if l < 0.5 else d / (2 - mx - mn)
            if mx == r:
                h = (g - b) / d + ( 6 if g < b else 0 )
            elif mx == g:
                h = (b - r) / d + 2
            else:
                h = r - g / d + 4

        return (int(round(h*60,4)), int(round(s*100,4)), int(round(l*100,4)))

    for i in r:
        # garyfeng: c_i could be rounded up so scl[c_i+1] will go off range
        #c_i = int(i*math.floor(SCL_FI)/round(r[-1])) # start color index
        #c_i = int(math.floor(i*math.floor(SCL_FI)/round(r[-1]))) # start color index
        #c_i = if c_i < len(scl)-1 else hsl_o

        c_i = int(math.floor(i))
        section_min = math.floor(i)
        section_max = math.ceil(i)
        fraction = (i-section_min) #/(section_max-section_min)

        hsl_o = rgb_to_hsl( scl[c_i] ) # convert rgb to hls
        hsl_f = rgb_to_hsl( scl[c_i+1] )
        #section_min = c_i*r[-1]/SCL_FI
        #section_max = (c_i+1)*(r[-1]/SCL_FI)
        #fraction = (i-section_min)/(section_max-section_min)
        hsl = interp3( fraction, hsl_o, hsl_f )
        c.append( 'hsl'+str(hsl) )

    return to_hsl( c )

[warpedgeoid]

I've just posted a duplicate as #13 .

[adavidzh]

Right now this problem is still in production.
If this was merged and fixed, can someone please make a new release in pypi? The present release (0.2.1) is from 2015: https://pypi.python.org/pypi/colorlover

[minroh]

I am having the same problem with colorlover version 0.2.1

colors = cl.interp(cl.scales['7']['qual']['Set2'], 61)

60 works, 68 works, some numbers in between do not work... Hope this gets fixed someday.

c:\users\user\appdata\local\programs\python\python36\lib\site-packages\colorlover_init_.py in interp(scl, r)
1821 c_i = int(imath.floor(SCL_FI)/round(r[-1])) # start color index
1822 hsl_o = rgb_to_hsl( scl[c_i] ) # convert rgb to hls
-> 1823 hsl_f = rgb_to_hsl( scl[c_i+1] )
1824 section_min = c_ir[-1]/SCL_FI
1825 section_max = (c_i+1)*(r[-1]/SCL_FI)

IndexError: list index out of range

[kengz]

this is not released, but one way around it is to install from source, the latest commit (locking version for safety). Then you'll get the updated interp function

pip install git+https://github.com/jackparmer/colorlover.git@d63b098530458223a985bef804ded0c9be9b00b2

[jonmmease]

Fixed by #9 and will be released in version 0.3