Cash as a portion of a pre-retirement portfolio
I am all for balanced portfolios, cash and bonds/cash/CDs, etc. (This discussion need not go into non-cash assets.) But in going over our accounts, I'm wondering about how much cash to carry, with retirement perhaps 5 years away. We have IRAs/401k's plus non-tax sheltered accounts. I think I shouldn't have cash or equivalents in the tax-sheltered accounts, and perhaps just have a year of expenses in cash in the regular accounts. Or should/could that be in income-producing instruments?
Any thought on how much cash as a proportion of assets one might carry into retirement?