[R-sig-Geo] Same code line for graph with different output messages

[Yuster Ronoh]

Dear r-geo members
Iam using example from creating maps with R by Robin Lovelace example  and
 I tried to plot map of active sport participant using the two codes, line
one gave me the error messages and line two gave me plot of active sport
partcipation in londe
1.plot(lnd_sport[lnd_sport$Partic_per > 25, ])
2.plot(lnd_sport[lnd_sport$Partic_Per > 25, ])
R-output
code for line 1
 > plot(lnd_sport[lnd_sport$Partic_per > 25, ])
Error in plot(lnd_sport[lnd_sport$Partic_per > 25, ]) :
  error in evaluating the argument 'x' in selecting a method for function
'plot': Error in if (is.numeric(i) && i < 0) { :
  missing value where TRUE/FALSE needed
code for line 2
 > plot(lnd_sport[lnd_sport$Partic_Per > 25, ]) # plotted actual graph
could some one explain what is happening

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