How to adjust list interval in xticks?

Question

I have data where I want to plot their timeseries. The FRQ is the column bar and the FILT is the line chart.

YEAR    FRQ FILT
1960    1   
1961    3   
1962    1   1.416666667
1963    1   0.916666667
1964    0   0.833333333
1965    1   1.333333333
1966    3   1.75
1967    2   1.5
1968    0   0.833333333
1969    0   0.666666667
1970    1   1.166666667
1971    3   1.666666667
1972    1   1.833333333
1973    2   1.75
1974    2   1.5
1975    1   1
1976    0   0.5
1977    0   0.416666667
1978    1   0.833333333
1979    1   1.333333333
1980    3   1.5
1981    0   1.333333333
1982    2   1
1983    0   0.833333333
1984    1   0.75
1985    1   0.583333333
1986    0   0.5
1987    0   0.75
1988    2   1.166666667
1989    2   1.25
1990    0   0.916666667
1991    1   0.833333333
1992    0   1.25
1993    4   1.5
1994    0   1.416666667
1995    1   1.25
1996    2   1.416666667
1997    1   1.833333333
1998    3   2
1999    2   1.75
2000    1   1.166666667
2001    0   1.083333333
2002    1   1.666666667
2003    5   2
2004    0   1.75
2005    1   1.5
2006    2   1.75
2007    3   2.166666667
2008    1   2.333333333
2009    4   2.333333333
2010    1   2.25
2011    3   1.916666667
2012    1   1.5
2013    1   1.166666667
2014    1   0.916666667
2015    1   0.75
2016    0   0.666666667
2017    1   0.75
2018    1   0.833333333
2019    1   
2020    0   

My working code looks like this:

#Read Tropical cyclone frequency 
TC = pd.read_csv (r'G:\TC_Atlas\\data.csv', encoding="ISO-8859-1")
TC = pd.DataFrame(TC,columns=['YEAR','FRQ','FILT','FRQ2','FILT2','LMI','FILTLMI','LMI2','FILTLMI2'])
TC=  TC[TC['YEAR'].between(1960,2020,inclusive="both")]
#TC = TC.set_index('YEAR')

labels =['1960','1961','1962','1963','1964','1965','1966','1967','1968','1969','1970','1971','1972','1973','1974','1975',
    '1976','1977','1978','1979','1980','1981','1982','1983','1984','1985','1986','1987','1988','1989','1990','1991','1992',
    '1993','1994','1995','1996','1997','1998','1999','2000','2001','2002','2003','2004','2005','2006','2007','2008','2009',
    '2010','2011','2012','2013','2014','2015','2016','2017','2018','2019','2020']

#Plot timeseries
TC['FRQ'].plot(kind='bar', color='lightgray', width=1, edgecolor='darkgray')
TC['FILT'].plot(kind='line',color='black')
plt.suptitle("TC Passage Frequency",fontweight='bold',y=0.95,x=0.53)
plt.title("Isabela (1960-2020)", pad=0)
L=plt.legend()
L.get_texts()[0].set_text('filtered')
plt.yticks(fontsize=12)
tickvalues = range(0,len(labels))
plt.xticks(ticks = tickvalues ,labels = labels, rotation = 30)

plt.xlabel('Year', color='black', fontsize=14, weight='bold',labelpad=10)
plt.ylabel('Frequency' , color='black', fontsize=14, weight='bold',labelpad=15)
plt.tight_layout()
plt.show()

Unfortunately, I cannot adjust the interval of the x-axis to make the xticks every 4 year interval. I have scouring for possible solution. Kindly help. I use Jupyter Notebook in Python. Below is the sample output but my goal is to make the xticks 4 year interval.

Answer 1

You are explicitly adding ticks every year. The culprit is this line:

plt.xticks(ticks = tickvalues ,labels = labels, rotation = 30)

To make them less frequent, you can take advantage of list slicing like so:

plt.xticks(ticks=tickvalues[::4], labels=labels[::4], rotation=30)

If you need to e.g. shift them so that a specific year is listed, you could set the initial index in the slice as well (e.g. tickvalues[2::4]).

EDIT: Since you are producing plots from a pd.DataFrame, a more sensible way would be using a column/index for ticks:

plt.xticks(TC['YEAR'][::4], rotation=30)

If your data is not converted properly, you might encounter weird bugs with ordering, in which case make sure you convert YEAR column to a number type by using astype or to_numeric first (a detailed writeup can be found in this SO answer).