Extract value and average

[Steven D'Aprano]

On Mon, 08 Jun 2009 18:13:50 +0200, Francesco Pietra wrote:

> I come 'naked', which is unusual and unfair.

???

> However, I find it
> difficult to give a correct start. The files consist, among other
> things, of a huge number of blocks of the type
> 
> 
>  NSTEP =     1000   TIME(PS) =     152.000  TEMP(K) =   298.54  PRESS = 
>    89.4 Etot   =   -134965.2123  EKtot   =     41282.1781  EPtot      = 
>   -176247.3905 BOND   =      1771.7644  ANGLE   =      6893.3003  DIHED 
>      =      4660.1650 1-4 NB =      1931.6071  1-4 EEL =      7799.8343 
>  VDWAALS    =     19047.1551 EELEC  =   -218354.9960  EHBOND  =        
>  0.0000  RESTRAINT  =         3.7793 EAMBER (non-restraint)  =  
>  -176251.1698 EKCMT  =     16048.2253  VIRIAL  =     14755.8154  VOLUME 
>     =    669299.5681
>                                                     Density    =        
>                                                     0.9896
>  Ewald error estimate:   0.8252E-05
> 
> 
> 
> (in attachment what surely is a correct reproduction of columns)
> 
> I would like to extract values corresponding to variable DIHED (here
> 4660.1650) and getting also the mean value from all DIHED.
> 
> Thanks for giving a possible attack


Assuming no DIHED value will ever be split over two lines:


data = open(filename)
values = []
for line in data:
    if line and line.strip():  # ignore blanks
         words = line.strip().split()
         try:
             i = words.index("DIHED")
         except IndexError:
             continue
         values.append(float(words[i+2]))
mean = sum(values)/len(values)


should do the job.


-- 
Steven