How do i annotate with a subscripted text in matplotlib?

Question

Im attempting to plot some data with matplotlib and i need some of the annotate to be formated like math/chem formulas. here is some of my code.

#!/usr/bin/python2 
import numpy as np
import matplotlib.pyplot as pytl
from matplotlib import rc
rc('font',**{'family':'sans-serif','sans-serif':['Helvetica']})
rc('text', usetex=True)
recdt = np.dtype([('compound',str,4),('H_v','f4'),('B_o','f4')]);
gat =  np.loadtxt('tra',dtype=object, usecols=(0,1,2),unpack=True);
gct,ght,gbt=[],[],[]
for c,h,b in np.transpose(gat):
    gct=np.append(gct,c)
    ght=np.append(ght,h)
    gbt=np.append(gbt,b)
ght= ght.astype(np.float)
gbt= gbt.astype(np.float)
hard = pytl
four = hard   #####  
four.scatter(gbt,ght)
hard.title( 'physical stuff' )
hard.xlabel('physical prop 1')
hard.ylabel('physical prop2 ')
for l,x1,y2 in zip ( gct,gbt,ght):
    hard.annotate( l,xy=(x1,y2),xytext=(-24,12),textcoords = 'offset points', arrowprops = dict(arrowstyle = '->', connectionstyle = 'arc3,rad=0'),rotation=0 )
hard.ylim([0,10])
hard.savefig('hardcomp.png')
hard.show()

and here is some test data

ZrC 6.8 1
NbC 8   2
NbN 7   13
RuB2    30  5
BP  3   1
AlP 9.4 3
InSb    2.2 47
C   6   4

the data is in three columns one text the other two are numbers. i'd like the '2' in 'RbB2' to end up as a subscript.

Answer 1

We can display the 2 in 'RbB2' with a subscript, by using TeX notation: $\\tt{RbB_{2}}$ . In the code, you just have to modify c :

import re
for c,h,b in np.transpose(gat):
    c = r'$\tt{{{c}}}$'.format(c = re.sub(r'(\d+)',r'_{\1}', c))

which yields

---

import re
import numpy as np
import matplotlib.pyplot as pytl
from matplotlib import rc

rc('font', **{'family':'sans-serif', 'sans-serif':['Helvetica']})
rc('text', usetex = True)
recdt = np.dtype([('compound', str, 4), ('H_v', 'f4'), ('B_o', 'f4')]);
gat =  np.loadtxt('tra', dtype = object, usecols = (0, 1, 2), unpack = True);
gct, ght, gbt = [], [], []
for c, h, b in np.transpose(gat):
    c = r'$\tt{{{c}}}$'.format(c = re.sub(r'(\d+)', r'_{\1}', c))
    gct = np.append(gct, c)
    ght = np.append(ght, h)
    gbt = np.append(gbt, b)
ght = ght.astype(np.float)
gbt = gbt.astype(np.float)
hard = pytl
four = hard   #####  
four.scatter(gbt, ght)
hard.title( 'physical stuff' )
hard.xlabel('physical prop 1')
hard.ylabel('physical prop2 ')
for l, x1, y2 in zip ( gct, gbt, ght):
    print(l, x1, y2)
    hard.annotate(
        l, xy = (x1, y2), xytext = (-24, 12), textcoords = 'offset points',
        arrowprops = dict(arrowstyle = '->', connectionstyle = 'arc3,rad=0'),
        rotation = 0 )
hard.ylim([0, 10])
hard.savefig('hardcomp.png')
hard.show()