def convert_period_into_pandas_freq(period_str):
	"""converts the period into a frequency format used by pandas library.

	Args:
	    period_str (string): period in string format using m, h and d to represent
	    minutes, hours and days.

	Returns:
	    string: new value for period according to pandas frequency format.
	    ex: 1m -> 1min, 1h -> 1H and 1d -> 1D
	"""
	number = ''.join(filter(str.isdigit, period_str))
	letter = ''.join(filter(str.isalpha, period_str))
	if letter == 'm':
		return ''.join([number, 'min'])
	# return uppercase of period_str for other values of letter
	return period_str.upper()