熊猫数据框到CSV将列更改为日期格式

Question

我有一个按日期索引的数据框，以便仅将某些年份输出到csv。我需要将2列连接到一个新列。但是，连接列的输出的前18行已更改为日期格式。

dates=[]
row=[]
col=[]
GHB_heads=[]
HEAD=[]
flux=[]
with open (fileloc, 'r') as fin:
    #print("reading in data")            
    data=fin.readlines()[1:]   
    for line in data:
        vals=line.split()
        date=vals[0][:10]
        dates.append(date)
        row.append(int(vals[6]))
        col.append(int(vals[7]))
        GHB_heads.append(float(vals[9]))
        HEAD.append(float(vals[10]))
        flux.append(float(vals[11]))
df=pd.DataFrame(list(zip(dates,row, col,GHB_heads,HEAD,flux)),columns=['Date','row','col','GHB_heads','HEAD','flux'])  
df['row_col']= df["row"].astype(str) + "-" + df["col"].astype(str)
df['Date'] =  pd.to_datetime(df['Date'], format='%Y-%m-%d')

y2016 = df[df['Date'].dt.year == 2016]    
y2067 = df[df['Date'].dt.year == 2067]

y2016.to_csv('GHB_LY9_2016.csv')
y2067.to_csv('GHB_LY9_2067.csv')

The csv output looks like this

My dataframe looks like this