pandas - Python: selecting columns for plotting based on values on rows

Question

I have a data frame that looks like

	Angle	1	2	3	4
Wavelength	20.5	677.8	445.76	345.76	987.5
1	56	432.56	123.65	545.76	456.65
2	67	9568.7	456.53	564.987	5675.4
3	62	9568.7	456.53	564.987	5675.4
5	72	9568.7	456.53	564.987	5675.4

question from:https://stackoverflow.com/questions/66061785/python-selecting-columns-for-plotting-based-on-values-on-rows

Answer 1

df.columns
# Index(['index', 'Angle', '1', '2', '3', '4'], dtype='object')


# step1. find row `Wavelength`
cond = df['index'] == 'Wavelength'
row = df[cond].iloc[0, 2:]
# row = df.loc[0, '1':]  # or use iloc -> df.iloc[0, 2:]

# step2. find which colums is closest to 500
cond = abs(row - 500) == abs(row - 500).min()
col = list(row[cond].index)

print(col) # ['2']

# as index is x-axis, col is y-axis
df.set_index('Angle')[col].plot()