Convert string data in HDF5 File to float Format - type-conversion

Question

I need to convert String data from a HDF5 File to Float format to use in a Skyplot (Astropy) with l b coordinates. The data is present here:
https://wwwmpa.mpa-garching.mpg.de/~ensslin/research/data/faraday2020.html
(Faraday Sky 2020)
The code I have programmed until now is:
from astropy import units as u
from astropy.coordinates import SkyCoord
import matplotlib.pyplot as plt
import numpy as np
import h5py
dat = []
ggl=[]
ggb=[]
f1= h5py.File('/home/nikita/faraday_2020/faraday2020.hdf5','r')
data = f1.get('faraday_sky_mean')
faraday_sky_mean = np.array(data)
data1 = f1.get('faraday_sky_std')
faraday_sky_std = np.array(data1)
n1 = 0
for line in f1:
s = line.split()
dat.append(s)
n1 = n1 +1
#
for i in range(0,n1):
ggl.append(float(dat[i][0])) # galactic coordinates input
ggb.append(float(dat[i][1]))
f1.close()
However I am getting the error:
ggl.append(float(dat[i][0])) # galactic coordinates input
ValueError: could not convert string to float: 'faraday_sky_mean'
Please help with this. Thanks.

Answer 1

What what you asked and what (I think) you need are 2 different things.
This line is NOT the way to read a HDF5 file: for line in f1:
You need to use a HDF5 API to read it (h5py is 1 of many).
I think you want to read datasets faraday_sky_mean and faraday_sky_std and load arrays into lists ggl and ggb. To do that, use this code. It will create 2 lists with 3145728 float64 values in each.
with h5py.File('faraday2020.hdf5','r') as hdf:
print(list(hdf.keys()))
faraday_sky_mean = hdf['faraday_sky_mean'][:]
faraday_sky_std = hdf['faraday_sky_std'][:]
print(faraday_sky_mean.shape, faraday_sky_mean.dtype)
print(f'Max Mean={max(faraday_sky_mean)}, Min Mean={min(faraday_sky_mean)}')
print(faraday_sky_std.shape, faraday_sky_std.dtype)
print(f'Max StdDev={max(faraday_sky_std)}, Min StdDev={min(faraday_sky_std)}')
ggl = faraday_sky_mean.tolist()
print(len(ggl),type(ggl[0]))
ggb = faraday_sky_std.tolist()
print(len(ggb),type(ggb[0]))
The procedure above saves the data as both NumPy arrays and Python lists. If you only need the lists (don't need the arrays), you can shorten the code as shown below:
with h5py.File('faraday2020.hdf5','r') as hdf:
ggl = hdf['faraday_sky_mean'][:].tolist()
print(len(ggl),type(ggl[0]))
ggb = hdf['faraday_sky_std'][:].tolist()
print(len(ggb),type(ggb[0]))