You cannot convert an empty string ('') to a float, as written in the error message. You have to convert this empty string to a float-like value beforehand: df_tmp['rain_1h'] = df_tmp['rain_1h'].replace('', '0').astype(float) for instance.

I've faced the same error while trying to create a heatmap. Following code solved my problem.

    hp_train.corr(numeric_only=True)

The following would be useful,

print (heterozygosity_df.columns)

This looks like static typing issue within pandas. What I suspect is heterozygosity_df.['chrI'] is a column in the dataframe. What I think has happened is there's a mix of strings and floats within this column. pandas has set this as a "string" but you are wanting to perform numerical operations. Thus the solution is simply

print(heterozygosity_df.dtypes) # this should state 'chrI' is a "category" or "string"
heterozygosity_df['chrI'] = heterozygosity_df['chrI'].astype(float)
print(heterozygosity_df.dtypes)

If you have multiple changes the syntax is

heterozygosity_df = heterozygosity_df.astype({'chrI':'float', 'egColumn':'category'})

I suspect there will be other errors, e.g. the header is the first row of the data column. This is because again for pandas to automatically assign a column to a "string" means there must be a string value within the column.

From the comments. I see whats happening. The easy solution is ...

replacement = {
    "chrI": 1,
    "chrII": 2,
    "chrIII": 3,
    "chrIV": 4,
    ....
}

heterozygosity_df['chr'] = heterozygosity_df['chr'].str.replace(replacement, regex=True)

From the comments ... good it works ... this is what I would have personally done ..

replacement = {
    "chrI": 1,
    "chrII": 2,
    "chrIII": 3,
    "chrIV": 4, # continue for all chromosomes
}

heterozygosity_df = pd.read_csv("file.tsv", sep="\t", header=None).set_axis(['chr', 'pos', 'het'], axis=1, copy=False)
heterozygosity_df['chr'] = heterozygosity_df['chr'].str.replace(replacement, regex=True).astype('int')

Normally str should be in place because when 'chr' is imported its an object. However, if it works thats the only thing that counts.