Convert strings of data to “Data” objects in R [duplicate]

This question already has an answer here:

as.Date with dates in format m/d/y in R 2 answers

My problem is that the as.Date function does not convert the values in a "date" column of a data frame into Date objects.

I have a data.frame nmmaps. Here is a short portion of it.

city     date death temp dewpoint     pm10       o3 time season

1 chic 1/1/1987   130 31.5   31.500 27.79119 4.025928    1 winter

2 chic 1/2/1987   150 33.0   29.875       NA 4.579652    2 winter

3 chic 1/3/1987   101 33.0   27.375 33.67382 3.400928    3 winter

4 chic 1/4/1987   135 29.0   28.625 40.79119 3.942595    4 winter

5 chic 1/5/1987   126 32.0   28.875       NA 4.400928    5 winter

6 chic 1/6/1987   130 40.0   35.125 41.79119 5.984261    6 winter

I imported the data from an Excel file with the following command:

nmmaps <- read.csv("chicago-nmmaps.csv" , as.is = T)

When I get to the point of converting by as.Date, I enter nmmaps$date <- as.Date(nmmaps$date) and get a data.frame shown below.

  city       date death temp dewpoint     pm10       o3 time season

1 chic 0001-01-19   130 31.5   31.500 27.79119 4.025928    1 winter

2 chic 0001-02-19   150 33.0   29.875       NA 4.579652    2 winter

3 chic 0001-03-19   101 33.0   27.375 33.67382 3.400928    3 winter

4 chic 0001-04-19   135 29.0   28.625 40.79119 3.942595    4 winter

5 chic 0001-05-19   126 32.0   28.875       NA 4.400928    5 winter

6 chic 0001-06-19   130 40.0   35.125 41.79119 5.984261    6 winter

Why are the dates shown this way? Also, some dates have a NA field. I would like the years to shown as 1987, 1988, 1989, etc..

Best How To :

If you read on the R help page for as.Date by typing ?as.Date you will see there is a default format assumed if you do not specify. So to specify for your data you would do

      nmmaps$date <- as.Date(nmmaps$date, format="%m/%d/%Y")

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