These charts reflect the results of the latest Quinnipiac University Poll of Iowa voters. It was done between October 30th and November 5th of 698 likely Democratic caucus attendees, and has a 4.5 point margin of error.
It shows four candidates leading the rest of the field -- Elizabeth Warren (20%), Pete Buttigieg (19%), Bernie Sanders (17%), and Joe Biden (15%). Considering the margin of error, those candidates are all very close and no real front-runner can be clearly shown. In other words, any of the four could win the state -- or they could divide the state's delegates fairly evenly.
It will be interesting to see how the next couple of months goes. Will one or two separate themselves, or will they stay bunched up?