help using grpstat() function
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load carbig
- Use the grpstats() function to find the mean, maximum and minimum MPG for cars manufactured in each year.
- Use an appropriate visualisation method to display the MPG data for each year. Does this data show a
trend? (i.e is MPG tending to increase/decrease over time?)
Q: returning errors when i process grpstats(x,MPG,'mean'), need some help please
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Geoff Hayes
2014-9-28
Andrew - what errors are you observing? Please include the complete error message and any (code) line number that it corresponds to.
采纳的回答
Sreeja Banerjee
2014-9-30
I understand that you are facing issues while trying to use the function "grpstats". The syntax for using the "grpstats" function is:
statarray = grpstats(tbl,groupvar,whichstats)
This syntax finds summary statistics specified in "whichstats" based on grouping variable "groupvar" for the data specified in "tbl". Thus, to find the mean, maximum and minimum MPG for cars manufactured in each year in the "carbig" dataset you have to use the following commands:
%%Statistics
meanMPG = grpstats(MPG,Model_Year,'mean');
maxMPG = grpstats(MPG,Model_Year,'max');
minMPG = grpstats(MPG,Model_Year,'min');
One way to visualize the MPG statistics by year is to use "errorbar". This function has the following syntax:
errorbar(X,Y,E)
Thus, for the dataset mentioned in this question, "Y" is the mean MPG which is plotted with respect to "X" or the Model_Year. The advantage of using this function is that the error "E" can be replaced with the standard deviation which is then plotted as an error bar. here is some code to do the same:
%%Code to visualize MPG statistics over time
stdMPG = grpstats(MPG,Model_Year,'std'); % Find standard deviation
errorbar(unique(Model_Year),meanMPG,stdMPG);
xlabel('Model year');
ylabel('MPG');
title('MPG over Time');
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