Help - Assigning monthly data to daily observations

Hey,
so I have daily data from 1.4.2009 to 31.12.2016. I need to add another variable, X, which only has values for monthly data, e.g. April 2009, May 2009 etc. Is there any function that can help me put the variable X to the daily observations, so that for every day I have one X variable value?

Example

april/09 ? april/09 4.32
april/09 ? mei/09 5.85
april/09 ? juni/09 -0.24
april/09 ? juli/09 4.78
april/09 ? augustus/09 1.06
april/09 ? september/09 2.18
april/09 ? oktober/09 -0.84
april/09 ? november/09 5.85
april/09 ? december/09 0.58

For every day in April/09 I need the value of 4.32 assigned, for every day in May/09 value 5.85 assigned etc.

Thank you in advance, I tried vlookup but it didnt work. I also thought about writing an IF function, but as I have over 3000 data it would be quite a fuss.

Any ideas?